linux/mm/memory-failure.c
Linus Torvalds 3d59eebc5e Automatic NUMA Balancing V11
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Merge tag 'balancenuma-v11' of git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux-balancenuma

Pull Automatic NUMA Balancing bare-bones from Mel Gorman:
 "There are three implementations for NUMA balancing, this tree
  (balancenuma), numacore which has been developed in tip/master and
  autonuma which is in aa.git.

  In almost all respects balancenuma is the dumbest of the three because
  its main impact is on the VM side with no attempt to be smart about
  scheduling.  In the interest of getting the ball rolling, it would be
  desirable to see this much merged for 3.8 with the view to building
  scheduler smarts on top and adapting the VM where required for 3.9.

  The most recent set of comparisons available from different people are

    mel:    https://lkml.org/lkml/2012/12/9/108
    mingo:  https://lkml.org/lkml/2012/12/7/331
    tglx:   https://lkml.org/lkml/2012/12/10/437
    srikar: https://lkml.org/lkml/2012/12/10/397

  The results are a mixed bag.  In my own tests, balancenuma does
  reasonably well.  It's dumb as rocks and does not regress against
  mainline.  On the other hand, Ingo's tests shows that balancenuma is
  incapable of converging for this workloads driven by perf which is bad
  but is potentially explained by the lack of scheduler smarts.  Thomas'
  results show balancenuma improves on mainline but falls far short of
  numacore or autonuma.  Srikar's results indicate we all suffer on a
  large machine with imbalanced node sizes.

  My own testing showed that recent numacore results have improved
  dramatically, particularly in the last week but not universally.
  We've butted heads heavily on system CPU usage and high levels of
  migration even when it shows that overall performance is better.
  There are also cases where it regresses.  Of interest is that for
  specjbb in some configurations it will regress for lower numbers of
  warehouses and show gains for higher numbers which is not reported by
  the tool by default and sometimes missed in treports.  Recently I
  reported for numacore that the JVM was crashing with
  NullPointerExceptions but currently it's unclear what the source of
  this problem is.  Initially I thought it was in how numacore batch
  handles PTEs but I'm no longer think this is the case.  It's possible
  numacore is just able to trigger it due to higher rates of migration.

  These reports were quite late in the cycle so I/we would like to start
  with this tree as it contains much of the code we can agree on and has
  not changed significantly over the last 2-3 weeks."

* tag 'balancenuma-v11' of git://git.kernel.org/pub/scm/linux/kernel/git/mel/linux-balancenuma: (50 commits)
  mm/rmap, migration: Make rmap_walk_anon() and try_to_unmap_anon() more scalable
  mm/rmap: Convert the struct anon_vma::mutex to an rwsem
  mm: migrate: Account a transhuge page properly when rate limiting
  mm: numa: Account for failed allocations and isolations as migration failures
  mm: numa: Add THP migration for the NUMA working set scanning fault case build fix
  mm: numa: Add THP migration for the NUMA working set scanning fault case.
  mm: sched: numa: Delay PTE scanning until a task is scheduled on a new node
  mm: sched: numa: Control enabling and disabling of NUMA balancing if !SCHED_DEBUG
  mm: sched: numa: Control enabling and disabling of NUMA balancing
  mm: sched: Adapt the scanning rate if a NUMA hinting fault does not migrate
  mm: numa: Use a two-stage filter to restrict pages being migrated for unlikely task<->node relationships
  mm: numa: migrate: Set last_nid on newly allocated page
  mm: numa: split_huge_page: Transfer last_nid on tail page
  mm: numa: Introduce last_nid to the page frame
  sched: numa: Slowly increase the scanning period as NUMA faults are handled
  mm: numa: Rate limit setting of pte_numa if node is saturated
  mm: numa: Rate limit the amount of memory that is migrated between nodes
  mm: numa: Structures for Migrate On Fault per NUMA migration rate limiting
  mm: numa: Migrate pages handled during a pmd_numa hinting fault
  mm: numa: Migrate on reference policy
  ...
2012-12-16 15:18:08 -08:00

1591 lines
42 KiB
C

/*
* Copyright (C) 2008, 2009 Intel Corporation
* Authors: Andi Kleen, Fengguang Wu
*
* This software may be redistributed and/or modified under the terms of
* the GNU General Public License ("GPL") version 2 only as published by the
* Free Software Foundation.
*
* High level machine check handler. Handles pages reported by the
* hardware as being corrupted usually due to a multi-bit ECC memory or cache
* failure.
*
* In addition there is a "soft offline" entry point that allows stop using
* not-yet-corrupted-by-suspicious pages without killing anything.
*
* Handles page cache pages in various states. The tricky part
* here is that we can access any page asynchronously in respect to
* other VM users, because memory failures could happen anytime and
* anywhere. This could violate some of their assumptions. This is why
* this code has to be extremely careful. Generally it tries to use
* normal locking rules, as in get the standard locks, even if that means
* the error handling takes potentially a long time.
*
* There are several operations here with exponential complexity because
* of unsuitable VM data structures. For example the operation to map back
* from RMAP chains to processes has to walk the complete process list and
* has non linear complexity with the number. But since memory corruptions
* are rare we hope to get away with this. This avoids impacting the core
* VM.
*/
/*
* Notebook:
* - hugetlb needs more code
* - kcore/oldmem/vmcore/mem/kmem check for hwpoison pages
* - pass bad pages to kdump next kernel
*/
#include <linux/kernel.h>
#include <linux/mm.h>
#include <linux/page-flags.h>
#include <linux/kernel-page-flags.h>
#include <linux/sched.h>
#include <linux/ksm.h>
#include <linux/rmap.h>
#include <linux/export.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/backing-dev.h>
#include <linux/migrate.h>
#include <linux/page-isolation.h>
#include <linux/suspend.h>
#include <linux/slab.h>
#include <linux/swapops.h>
#include <linux/hugetlb.h>
#include <linux/memory_hotplug.h>
#include <linux/mm_inline.h>
#include <linux/kfifo.h>
#include "internal.h"
int sysctl_memory_failure_early_kill __read_mostly = 0;
int sysctl_memory_failure_recovery __read_mostly = 1;
atomic_long_t mce_bad_pages __read_mostly = ATOMIC_LONG_INIT(0);
#if defined(CONFIG_HWPOISON_INJECT) || defined(CONFIG_HWPOISON_INJECT_MODULE)
u32 hwpoison_filter_enable = 0;
u32 hwpoison_filter_dev_major = ~0U;
u32 hwpoison_filter_dev_minor = ~0U;
u64 hwpoison_filter_flags_mask;
u64 hwpoison_filter_flags_value;
EXPORT_SYMBOL_GPL(hwpoison_filter_enable);
EXPORT_SYMBOL_GPL(hwpoison_filter_dev_major);
EXPORT_SYMBOL_GPL(hwpoison_filter_dev_minor);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_mask);
EXPORT_SYMBOL_GPL(hwpoison_filter_flags_value);
static int hwpoison_filter_dev(struct page *p)
{
struct address_space *mapping;
dev_t dev;
if (hwpoison_filter_dev_major == ~0U &&
hwpoison_filter_dev_minor == ~0U)
return 0;
/*
* page_mapping() does not accept slab pages.
*/
if (PageSlab(p))
return -EINVAL;
mapping = page_mapping(p);
if (mapping == NULL || mapping->host == NULL)
return -EINVAL;
dev = mapping->host->i_sb->s_dev;
if (hwpoison_filter_dev_major != ~0U &&
hwpoison_filter_dev_major != MAJOR(dev))
return -EINVAL;
if (hwpoison_filter_dev_minor != ~0U &&
hwpoison_filter_dev_minor != MINOR(dev))
return -EINVAL;
return 0;
}
static int hwpoison_filter_flags(struct page *p)
{
if (!hwpoison_filter_flags_mask)
return 0;
if ((stable_page_flags(p) & hwpoison_filter_flags_mask) ==
hwpoison_filter_flags_value)
return 0;
else
return -EINVAL;
}
/*
* This allows stress tests to limit test scope to a collection of tasks
* by putting them under some memcg. This prevents killing unrelated/important
* processes such as /sbin/init. Note that the target task may share clean
* pages with init (eg. libc text), which is harmless. If the target task
* share _dirty_ pages with another task B, the test scheme must make sure B
* is also included in the memcg. At last, due to race conditions this filter
* can only guarantee that the page either belongs to the memcg tasks, or is
* a freed page.
*/
#ifdef CONFIG_MEMCG_SWAP
u64 hwpoison_filter_memcg;
EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
static int hwpoison_filter_task(struct page *p)
{
struct mem_cgroup *mem;
struct cgroup_subsys_state *css;
unsigned long ino;
if (!hwpoison_filter_memcg)
return 0;
mem = try_get_mem_cgroup_from_page(p);
if (!mem)
return -EINVAL;
css = mem_cgroup_css(mem);
/* root_mem_cgroup has NULL dentries */
if (!css->cgroup->dentry)
return -EINVAL;
ino = css->cgroup->dentry->d_inode->i_ino;
css_put(css);
if (ino != hwpoison_filter_memcg)
return -EINVAL;
return 0;
}
#else
static int hwpoison_filter_task(struct page *p) { return 0; }
#endif
int hwpoison_filter(struct page *p)
{
if (!hwpoison_filter_enable)
return 0;
if (hwpoison_filter_dev(p))
return -EINVAL;
if (hwpoison_filter_flags(p))
return -EINVAL;
if (hwpoison_filter_task(p))
return -EINVAL;
return 0;
}
#else
int hwpoison_filter(struct page *p)
{
return 0;
}
#endif
EXPORT_SYMBOL_GPL(hwpoison_filter);
/*
* Send all the processes who have the page mapped a signal.
* ``action optional'' if they are not immediately affected by the error
* ``action required'' if error happened in current execution context
*/
static int kill_proc(struct task_struct *t, unsigned long addr, int trapno,
unsigned long pfn, struct page *page, int flags)
{
struct siginfo si;
int ret;
printk(KERN_ERR
"MCE %#lx: Killing %s:%d due to hardware memory corruption\n",
pfn, t->comm, t->pid);
si.si_signo = SIGBUS;
si.si_errno = 0;
si.si_addr = (void *)addr;
#ifdef __ARCH_SI_TRAPNO
si.si_trapno = trapno;
#endif
si.si_addr_lsb = compound_trans_order(compound_head(page)) + PAGE_SHIFT;
if ((flags & MF_ACTION_REQUIRED) && t == current) {
si.si_code = BUS_MCEERR_AR;
ret = force_sig_info(SIGBUS, &si, t);
} else {
/*
* Don't use force here, it's convenient if the signal
* can be temporarily blocked.
* This could cause a loop when the user sets SIGBUS
* to SIG_IGN, but hopefully no one will do that?
*/
si.si_code = BUS_MCEERR_AO;
ret = send_sig_info(SIGBUS, &si, t); /* synchronous? */
}
if (ret < 0)
printk(KERN_INFO "MCE: Error sending signal to %s:%d: %d\n",
t->comm, t->pid, ret);
return ret;
}
/*
* When a unknown page type is encountered drain as many buffers as possible
* in the hope to turn the page into a LRU or free page, which we can handle.
*/
void shake_page(struct page *p, int access)
{
if (!PageSlab(p)) {
lru_add_drain_all();
if (PageLRU(p))
return;
drain_all_pages();
if (PageLRU(p) || is_free_buddy_page(p))
return;
}
/*
* Only call shrink_slab here (which would also shrink other caches) if
* access is not potentially fatal.
*/
if (access) {
int nr;
do {
struct shrink_control shrink = {
.gfp_mask = GFP_KERNEL,
};
nr = shrink_slab(&shrink, 1000, 1000);
if (page_count(p) == 1)
break;
} while (nr > 10);
}
}
EXPORT_SYMBOL_GPL(shake_page);
/*
* Kill all processes that have a poisoned page mapped and then isolate
* the page.
*
* General strategy:
* Find all processes having the page mapped and kill them.
* But we keep a page reference around so that the page is not
* actually freed yet.
* Then stash the page away
*
* There's no convenient way to get back to mapped processes
* from the VMAs. So do a brute-force search over all
* running processes.
*
* Remember that machine checks are not common (or rather
* if they are common you have other problems), so this shouldn't
* be a performance issue.
*
* Also there are some races possible while we get from the
* error detection to actually handle it.
*/
struct to_kill {
struct list_head nd;
struct task_struct *tsk;
unsigned long addr;
char addr_valid;
};
/*
* Failure handling: if we can't find or can't kill a process there's
* not much we can do. We just print a message and ignore otherwise.
*/
/*
* Schedule a process for later kill.
* Uses GFP_ATOMIC allocations to avoid potential recursions in the VM.
* TBD would GFP_NOIO be enough?
*/
static void add_to_kill(struct task_struct *tsk, struct page *p,
struct vm_area_struct *vma,
struct list_head *to_kill,
struct to_kill **tkc)
{
struct to_kill *tk;
if (*tkc) {
tk = *tkc;
*tkc = NULL;
} else {
tk = kmalloc(sizeof(struct to_kill), GFP_ATOMIC);
if (!tk) {
printk(KERN_ERR
"MCE: Out of memory while machine check handling\n");
return;
}
}
tk->addr = page_address_in_vma(p, vma);
tk->addr_valid = 1;
/*
* In theory we don't have to kill when the page was
* munmaped. But it could be also a mremap. Since that's
* likely very rare kill anyways just out of paranoia, but use
* a SIGKILL because the error is not contained anymore.
*/
if (tk->addr == -EFAULT) {
pr_info("MCE: Unable to find user space address %lx in %s\n",
page_to_pfn(p), tsk->comm);
tk->addr_valid = 0;
}
get_task_struct(tsk);
tk->tsk = tsk;
list_add_tail(&tk->nd, to_kill);
}
/*
* Kill the processes that have been collected earlier.
*
* Only do anything when DOIT is set, otherwise just free the list
* (this is used for clean pages which do not need killing)
* Also when FAIL is set do a force kill because something went
* wrong earlier.
*/
static void kill_procs(struct list_head *to_kill, int forcekill, int trapno,
int fail, struct page *page, unsigned long pfn,
int flags)
{
struct to_kill *tk, *next;
list_for_each_entry_safe (tk, next, to_kill, nd) {
if (forcekill) {
/*
* In case something went wrong with munmapping
* make sure the process doesn't catch the
* signal and then access the memory. Just kill it.
*/
if (fail || tk->addr_valid == 0) {
printk(KERN_ERR
"MCE %#lx: forcibly killing %s:%d because of failure to unmap corrupted page\n",
pfn, tk->tsk->comm, tk->tsk->pid);
force_sig(SIGKILL, tk->tsk);
}
/*
* In theory the process could have mapped
* something else on the address in-between. We could
* check for that, but we need to tell the
* process anyways.
*/
else if (kill_proc(tk->tsk, tk->addr, trapno,
pfn, page, flags) < 0)
printk(KERN_ERR
"MCE %#lx: Cannot send advisory machine check signal to %s:%d\n",
pfn, tk->tsk->comm, tk->tsk->pid);
}
put_task_struct(tk->tsk);
kfree(tk);
}
}
static int task_early_kill(struct task_struct *tsk)
{
if (!tsk->mm)
return 0;
if (tsk->flags & PF_MCE_PROCESS)
return !!(tsk->flags & PF_MCE_EARLY);
return sysctl_memory_failure_early_kill;
}
/*
* Collect processes when the error hit an anonymous page.
*/
static void collect_procs_anon(struct page *page, struct list_head *to_kill,
struct to_kill **tkc)
{
struct vm_area_struct *vma;
struct task_struct *tsk;
struct anon_vma *av;
pgoff_t pgoff;
av = page_lock_anon_vma_read(page);
if (av == NULL) /* Not actually mapped anymore */
return;
pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
read_lock(&tasklist_lock);
for_each_process (tsk) {
struct anon_vma_chain *vmac;
if (!task_early_kill(tsk))
continue;
anon_vma_interval_tree_foreach(vmac, &av->rb_root,
pgoff, pgoff) {
vma = vmac->vma;
if (!page_mapped_in_vma(page, vma))
continue;
if (vma->vm_mm == tsk->mm)
add_to_kill(tsk, page, vma, to_kill, tkc);
}
}
read_unlock(&tasklist_lock);
page_unlock_anon_vma_read(av);
}
/*
* Collect processes when the error hit a file mapped page.
*/
static void collect_procs_file(struct page *page, struct list_head *to_kill,
struct to_kill **tkc)
{
struct vm_area_struct *vma;
struct task_struct *tsk;
struct address_space *mapping = page->mapping;
mutex_lock(&mapping->i_mmap_mutex);
read_lock(&tasklist_lock);
for_each_process(tsk) {
pgoff_t pgoff = page->index << (PAGE_CACHE_SHIFT - PAGE_SHIFT);
if (!task_early_kill(tsk))
continue;
vma_interval_tree_foreach(vma, &mapping->i_mmap, pgoff,
pgoff) {
/*
* Send early kill signal to tasks where a vma covers
* the page but the corrupted page is not necessarily
* mapped it in its pte.
* Assume applications who requested early kill want
* to be informed of all such data corruptions.
*/
if (vma->vm_mm == tsk->mm)
add_to_kill(tsk, page, vma, to_kill, tkc);
}
}
read_unlock(&tasklist_lock);
mutex_unlock(&mapping->i_mmap_mutex);
}
/*
* Collect the processes who have the corrupted page mapped to kill.
* This is done in two steps for locking reasons.
* First preallocate one tokill structure outside the spin locks,
* so that we can kill at least one process reasonably reliable.
*/
static void collect_procs(struct page *page, struct list_head *tokill)
{
struct to_kill *tk;
if (!page->mapping)
return;
tk = kmalloc(sizeof(struct to_kill), GFP_NOIO);
if (!tk)
return;
if (PageAnon(page))
collect_procs_anon(page, tokill, &tk);
else
collect_procs_file(page, tokill, &tk);
kfree(tk);
}
/*
* Error handlers for various types of pages.
*/
enum outcome {
IGNORED, /* Error: cannot be handled */
FAILED, /* Error: handling failed */
DELAYED, /* Will be handled later */
RECOVERED, /* Successfully recovered */
};
static const char *action_name[] = {
[IGNORED] = "Ignored",
[FAILED] = "Failed",
[DELAYED] = "Delayed",
[RECOVERED] = "Recovered",
};
/*
* XXX: It is possible that a page is isolated from LRU cache,
* and then kept in swap cache or failed to remove from page cache.
* The page count will stop it from being freed by unpoison.
* Stress tests should be aware of this memory leak problem.
*/
static int delete_from_lru_cache(struct page *p)
{
if (!isolate_lru_page(p)) {
/*
* Clear sensible page flags, so that the buddy system won't
* complain when the page is unpoison-and-freed.
*/
ClearPageActive(p);
ClearPageUnevictable(p);
/*
* drop the page count elevated by isolate_lru_page()
*/
page_cache_release(p);
return 0;
}
return -EIO;
}
/*
* Error hit kernel page.
* Do nothing, try to be lucky and not touch this instead. For a few cases we
* could be more sophisticated.
*/
static int me_kernel(struct page *p, unsigned long pfn)
{
return IGNORED;
}
/*
* Page in unknown state. Do nothing.
*/
static int me_unknown(struct page *p, unsigned long pfn)
{
printk(KERN_ERR "MCE %#lx: Unknown page state\n", pfn);
return FAILED;
}
/*
* Clean (or cleaned) page cache page.
*/
static int me_pagecache_clean(struct page *p, unsigned long pfn)
{
int err;
int ret = FAILED;
struct address_space *mapping;
delete_from_lru_cache(p);
/*
* For anonymous pages we're done the only reference left
* should be the one m_f() holds.
*/
if (PageAnon(p))
return RECOVERED;
/*
* Now truncate the page in the page cache. This is really
* more like a "temporary hole punch"
* Don't do this for block devices when someone else
* has a reference, because it could be file system metadata
* and that's not safe to truncate.
*/
mapping = page_mapping(p);
if (!mapping) {
/*
* Page has been teared down in the meanwhile
*/
return FAILED;
}
/*
* Truncation is a bit tricky. Enable it per file system for now.
*
* Open: to take i_mutex or not for this? Right now we don't.
*/
if (mapping->a_ops->error_remove_page) {
err = mapping->a_ops->error_remove_page(mapping, p);
if (err != 0) {
printk(KERN_INFO "MCE %#lx: Failed to punch page: %d\n",
pfn, err);
} else if (page_has_private(p) &&
!try_to_release_page(p, GFP_NOIO)) {
pr_info("MCE %#lx: failed to release buffers\n", pfn);
} else {
ret = RECOVERED;
}
} else {
/*
* If the file system doesn't support it just invalidate
* This fails on dirty or anything with private pages
*/
if (invalidate_inode_page(p))
ret = RECOVERED;
else
printk(KERN_INFO "MCE %#lx: Failed to invalidate\n",
pfn);
}
return ret;
}
/*
* Dirty cache page page
* Issues: when the error hit a hole page the error is not properly
* propagated.
*/
static int me_pagecache_dirty(struct page *p, unsigned long pfn)
{
struct address_space *mapping = page_mapping(p);
SetPageError(p);
/* TBD: print more information about the file. */
if (mapping) {
/*
* IO error will be reported by write(), fsync(), etc.
* who check the mapping.
* This way the application knows that something went
* wrong with its dirty file data.
*
* There's one open issue:
*
* The EIO will be only reported on the next IO
* operation and then cleared through the IO map.
* Normally Linux has two mechanisms to pass IO error
* first through the AS_EIO flag in the address space
* and then through the PageError flag in the page.
* Since we drop pages on memory failure handling the
* only mechanism open to use is through AS_AIO.
*
* This has the disadvantage that it gets cleared on
* the first operation that returns an error, while
* the PageError bit is more sticky and only cleared
* when the page is reread or dropped. If an
* application assumes it will always get error on
* fsync, but does other operations on the fd before
* and the page is dropped between then the error
* will not be properly reported.
*
* This can already happen even without hwpoisoned
* pages: first on metadata IO errors (which only
* report through AS_EIO) or when the page is dropped
* at the wrong time.
*
* So right now we assume that the application DTRT on
* the first EIO, but we're not worse than other parts
* of the kernel.
*/
mapping_set_error(mapping, EIO);
}
return me_pagecache_clean(p, pfn);
}
/*
* Clean and dirty swap cache.
*
* Dirty swap cache page is tricky to handle. The page could live both in page
* cache and swap cache(ie. page is freshly swapped in). So it could be
* referenced concurrently by 2 types of PTEs:
* normal PTEs and swap PTEs. We try to handle them consistently by calling
* try_to_unmap(TTU_IGNORE_HWPOISON) to convert the normal PTEs to swap PTEs,
* and then
* - clear dirty bit to prevent IO
* - remove from LRU
* - but keep in the swap cache, so that when we return to it on
* a later page fault, we know the application is accessing
* corrupted data and shall be killed (we installed simple
* interception code in do_swap_page to catch it).
*
* Clean swap cache pages can be directly isolated. A later page fault will
* bring in the known good data from disk.
*/
static int me_swapcache_dirty(struct page *p, unsigned long pfn)
{
ClearPageDirty(p);
/* Trigger EIO in shmem: */
ClearPageUptodate(p);
if (!delete_from_lru_cache(p))
return DELAYED;
else
return FAILED;
}
static int me_swapcache_clean(struct page *p, unsigned long pfn)
{
delete_from_swap_cache(p);
if (!delete_from_lru_cache(p))
return RECOVERED;
else
return FAILED;
}
/*
* Huge pages. Needs work.
* Issues:
* - Error on hugepage is contained in hugepage unit (not in raw page unit.)
* To narrow down kill region to one page, we need to break up pmd.
*/
static int me_huge_page(struct page *p, unsigned long pfn)
{
int res = 0;
struct page *hpage = compound_head(p);
/*
* We can safely recover from error on free or reserved (i.e.
* not in-use) hugepage by dequeuing it from freelist.
* To check whether a hugepage is in-use or not, we can't use
* page->lru because it can be used in other hugepage operations,
* such as __unmap_hugepage_range() and gather_surplus_pages().
* So instead we use page_mapping() and PageAnon().
* We assume that this function is called with page lock held,
* so there is no race between isolation and mapping/unmapping.
*/
if (!(page_mapping(hpage) || PageAnon(hpage))) {
res = dequeue_hwpoisoned_huge_page(hpage);
if (!res)
return RECOVERED;
}
return DELAYED;
}
/*
* Various page states we can handle.
*
* A page state is defined by its current page->flags bits.
* The table matches them in order and calls the right handler.
*
* This is quite tricky because we can access page at any time
* in its live cycle, so all accesses have to be extremely careful.
*
* This is not complete. More states could be added.
* For any missing state don't attempt recovery.
*/
#define dirty (1UL << PG_dirty)
#define sc (1UL << PG_swapcache)
#define unevict (1UL << PG_unevictable)
#define mlock (1UL << PG_mlocked)
#define writeback (1UL << PG_writeback)
#define lru (1UL << PG_lru)
#define swapbacked (1UL << PG_swapbacked)
#define head (1UL << PG_head)
#define tail (1UL << PG_tail)
#define compound (1UL << PG_compound)
#define slab (1UL << PG_slab)
#define reserved (1UL << PG_reserved)
static struct page_state {
unsigned long mask;
unsigned long res;
char *msg;
int (*action)(struct page *p, unsigned long pfn);
} error_states[] = {
{ reserved, reserved, "reserved kernel", me_kernel },
/*
* free pages are specially detected outside this table:
* PG_buddy pages only make a small fraction of all free pages.
*/
/*
* Could in theory check if slab page is free or if we can drop
* currently unused objects without touching them. But just
* treat it as standard kernel for now.
*/
{ slab, slab, "kernel slab", me_kernel },
#ifdef CONFIG_PAGEFLAGS_EXTENDED
{ head, head, "huge", me_huge_page },
{ tail, tail, "huge", me_huge_page },
#else
{ compound, compound, "huge", me_huge_page },
#endif
{ sc|dirty, sc|dirty, "dirty swapcache", me_swapcache_dirty },
{ sc|dirty, sc, "clean swapcache", me_swapcache_clean },
{ unevict|dirty, unevict|dirty, "dirty unevictable LRU", me_pagecache_dirty },
{ unevict, unevict, "clean unevictable LRU", me_pagecache_clean },
{ mlock|dirty, mlock|dirty, "dirty mlocked LRU", me_pagecache_dirty },
{ mlock, mlock, "clean mlocked LRU", me_pagecache_clean },
{ lru|dirty, lru|dirty, "dirty LRU", me_pagecache_dirty },
{ lru|dirty, lru, "clean LRU", me_pagecache_clean },
/*
* Catchall entry: must be at end.
*/
{ 0, 0, "unknown page state", me_unknown },
};
#undef dirty
#undef sc
#undef unevict
#undef mlock
#undef writeback
#undef lru
#undef swapbacked
#undef head
#undef tail
#undef compound
#undef slab
#undef reserved
/*
* "Dirty/Clean" indication is not 100% accurate due to the possibility of
* setting PG_dirty outside page lock. See also comment above set_page_dirty().
*/
static void action_result(unsigned long pfn, char *msg, int result)
{
pr_err("MCE %#lx: %s page recovery: %s\n",
pfn, msg, action_name[result]);
}
static int page_action(struct page_state *ps, struct page *p,
unsigned long pfn)
{
int result;
int count;
result = ps->action(p, pfn);
action_result(pfn, ps->msg, result);
count = page_count(p) - 1;
if (ps->action == me_swapcache_dirty && result == DELAYED)
count--;
if (count != 0) {
printk(KERN_ERR
"MCE %#lx: %s page still referenced by %d users\n",
pfn, ps->msg, count);
result = FAILED;
}
/* Could do more checks here if page looks ok */
/*
* Could adjust zone counters here to correct for the missing page.
*/
return (result == RECOVERED || result == DELAYED) ? 0 : -EBUSY;
}
/*
* Do all that is necessary to remove user space mappings. Unmap
* the pages and send SIGBUS to the processes if the data was dirty.
*/
static int hwpoison_user_mappings(struct page *p, unsigned long pfn,
int trapno, int flags)
{
enum ttu_flags ttu = TTU_UNMAP | TTU_IGNORE_MLOCK | TTU_IGNORE_ACCESS;
struct address_space *mapping;
LIST_HEAD(tokill);
int ret;
int kill = 1, forcekill;
struct page *hpage = compound_head(p);
struct page *ppage;
if (PageReserved(p) || PageSlab(p))
return SWAP_SUCCESS;
/*
* This check implies we don't kill processes if their pages
* are in the swap cache early. Those are always late kills.
*/
if (!page_mapped(hpage))
return SWAP_SUCCESS;
if (PageKsm(p))
return SWAP_FAIL;
if (PageSwapCache(p)) {
printk(KERN_ERR
"MCE %#lx: keeping poisoned page in swap cache\n", pfn);
ttu |= TTU_IGNORE_HWPOISON;
}
/*
* Propagate the dirty bit from PTEs to struct page first, because we
* need this to decide if we should kill or just drop the page.
* XXX: the dirty test could be racy: set_page_dirty() may not always
* be called inside page lock (it's recommended but not enforced).
*/
mapping = page_mapping(hpage);
if (!(flags & MF_MUST_KILL) && !PageDirty(hpage) && mapping &&
mapping_cap_writeback_dirty(mapping)) {
if (page_mkclean(hpage)) {
SetPageDirty(hpage);
} else {
kill = 0;
ttu |= TTU_IGNORE_HWPOISON;
printk(KERN_INFO
"MCE %#lx: corrupted page was clean: dropped without side effects\n",
pfn);
}
}
/*
* ppage: poisoned page
* if p is regular page(4k page)
* ppage == real poisoned page;
* else p is hugetlb or THP, ppage == head page.
*/
ppage = hpage;
if (PageTransHuge(hpage)) {
/*
* Verify that this isn't a hugetlbfs head page, the check for
* PageAnon is just for avoid tripping a split_huge_page
* internal debug check, as split_huge_page refuses to deal with
* anything that isn't an anon page. PageAnon can't go away fro
* under us because we hold a refcount on the hpage, without a
* refcount on the hpage. split_huge_page can't be safely called
* in the first place, having a refcount on the tail isn't
* enough * to be safe.
*/
if (!PageHuge(hpage) && PageAnon(hpage)) {
if (unlikely(split_huge_page(hpage))) {
/*
* FIXME: if splitting THP is failed, it is
* better to stop the following operation rather
* than causing panic by unmapping. System might
* survive if the page is freed later.
*/
printk(KERN_INFO
"MCE %#lx: failed to split THP\n", pfn);
BUG_ON(!PageHWPoison(p));
return SWAP_FAIL;
}
/* THP is split, so ppage should be the real poisoned page. */
ppage = p;
}
}
/*
* First collect all the processes that have the page
* mapped in dirty form. This has to be done before try_to_unmap,
* because ttu takes the rmap data structures down.
*
* Error handling: We ignore errors here because
* there's nothing that can be done.
*/
if (kill)
collect_procs(ppage, &tokill);
if (hpage != ppage)
lock_page(ppage);
ret = try_to_unmap(ppage, ttu);
if (ret != SWAP_SUCCESS)
printk(KERN_ERR "MCE %#lx: failed to unmap page (mapcount=%d)\n",
pfn, page_mapcount(ppage));
if (hpage != ppage)
unlock_page(ppage);
/*
* Now that the dirty bit has been propagated to the
* struct page and all unmaps done we can decide if
* killing is needed or not. Only kill when the page
* was dirty or the process is not restartable,
* otherwise the tokill list is merely
* freed. When there was a problem unmapping earlier
* use a more force-full uncatchable kill to prevent
* any accesses to the poisoned memory.
*/
forcekill = PageDirty(ppage) || (flags & MF_MUST_KILL);
kill_procs(&tokill, forcekill, trapno,
ret != SWAP_SUCCESS, p, pfn, flags);
return ret;
}
static void set_page_hwpoison_huge_page(struct page *hpage)
{
int i;
int nr_pages = 1 << compound_trans_order(hpage);
for (i = 0; i < nr_pages; i++)
SetPageHWPoison(hpage + i);
}
static void clear_page_hwpoison_huge_page(struct page *hpage)
{
int i;
int nr_pages = 1 << compound_trans_order(hpage);
for (i = 0; i < nr_pages; i++)
ClearPageHWPoison(hpage + i);
}
/**
* memory_failure - Handle memory failure of a page.
* @pfn: Page Number of the corrupted page
* @trapno: Trap number reported in the signal to user space.
* @flags: fine tune action taken
*
* This function is called by the low level machine check code
* of an architecture when it detects hardware memory corruption
* of a page. It tries its best to recover, which includes
* dropping pages, killing processes etc.
*
* The function is primarily of use for corruptions that
* happen outside the current execution context (e.g. when
* detected by a background scrubber)
*
* Must run in process context (e.g. a work queue) with interrupts
* enabled and no spinlocks hold.
*/
int memory_failure(unsigned long pfn, int trapno, int flags)
{
struct page_state *ps;
struct page *p;
struct page *hpage;
int res;
unsigned int nr_pages;
if (!sysctl_memory_failure_recovery)
panic("Memory failure from trap %d on page %lx", trapno, pfn);
if (!pfn_valid(pfn)) {
printk(KERN_ERR
"MCE %#lx: memory outside kernel control\n",
pfn);
return -ENXIO;
}
p = pfn_to_page(pfn);
hpage = compound_head(p);
if (TestSetPageHWPoison(p)) {
printk(KERN_ERR "MCE %#lx: already hardware poisoned\n", pfn);
return 0;
}
nr_pages = 1 << compound_trans_order(hpage);
atomic_long_add(nr_pages, &mce_bad_pages);
/*
* We need/can do nothing about count=0 pages.
* 1) it's a free page, and therefore in safe hand:
* prep_new_page() will be the gate keeper.
* 2) it's a free hugepage, which is also safe:
* an affected hugepage will be dequeued from hugepage freelist,
* so there's no concern about reusing it ever after.
* 3) it's part of a non-compound high order page.
* Implies some kernel user: cannot stop them from
* R/W the page; let's pray that the page has been
* used and will be freed some time later.
* In fact it's dangerous to directly bump up page count from 0,
* that may make page_freeze_refs()/page_unfreeze_refs() mismatch.
*/
if (!(flags & MF_COUNT_INCREASED) &&
!get_page_unless_zero(hpage)) {
if (is_free_buddy_page(p)) {
action_result(pfn, "free buddy", DELAYED);
return 0;
} else if (PageHuge(hpage)) {
/*
* Check "just unpoisoned", "filter hit", and
* "race with other subpage."
*/
lock_page(hpage);
if (!PageHWPoison(hpage)
|| (hwpoison_filter(p) && TestClearPageHWPoison(p))
|| (p != hpage && TestSetPageHWPoison(hpage))) {
atomic_long_sub(nr_pages, &mce_bad_pages);
return 0;
}
set_page_hwpoison_huge_page(hpage);
res = dequeue_hwpoisoned_huge_page(hpage);
action_result(pfn, "free huge",
res ? IGNORED : DELAYED);
unlock_page(hpage);
return res;
} else {
action_result(pfn, "high order kernel", IGNORED);
return -EBUSY;
}
}
/*
* We ignore non-LRU pages for good reasons.
* - PG_locked is only well defined for LRU pages and a few others
* - to avoid races with __set_page_locked()
* - to avoid races with __SetPageSlab*() (and more non-atomic ops)
* The check (unnecessarily) ignores LRU pages being isolated and
* walked by the page reclaim code, however that's not a big loss.
*/
if (!PageHuge(p) && !PageTransTail(p)) {
if (!PageLRU(p))
shake_page(p, 0);
if (!PageLRU(p)) {
/*
* shake_page could have turned it free.
*/
if (is_free_buddy_page(p)) {
action_result(pfn, "free buddy, 2nd try",
DELAYED);
return 0;
}
action_result(pfn, "non LRU", IGNORED);
put_page(p);
return -EBUSY;
}
}
/*
* Lock the page and wait for writeback to finish.
* It's very difficult to mess with pages currently under IO
* and in many cases impossible, so we just avoid it here.
*/
lock_page(hpage);
/*
* unpoison always clear PG_hwpoison inside page lock
*/
if (!PageHWPoison(p)) {
printk(KERN_ERR "MCE %#lx: just unpoisoned\n", pfn);
res = 0;
goto out;
}
if (hwpoison_filter(p)) {
if (TestClearPageHWPoison(p))
atomic_long_sub(nr_pages, &mce_bad_pages);
unlock_page(hpage);
put_page(hpage);
return 0;
}
/*
* For error on the tail page, we should set PG_hwpoison
* on the head page to show that the hugepage is hwpoisoned
*/
if (PageHuge(p) && PageTail(p) && TestSetPageHWPoison(hpage)) {
action_result(pfn, "hugepage already hardware poisoned",
IGNORED);
unlock_page(hpage);
put_page(hpage);
return 0;
}
/*
* Set PG_hwpoison on all pages in an error hugepage,
* because containment is done in hugepage unit for now.
* Since we have done TestSetPageHWPoison() for the head page with
* page lock held, we can safely set PG_hwpoison bits on tail pages.
*/
if (PageHuge(p))
set_page_hwpoison_huge_page(hpage);
wait_on_page_writeback(p);
/*
* Now take care of user space mappings.
* Abort on fail: __delete_from_page_cache() assumes unmapped page.
*/
if (hwpoison_user_mappings(p, pfn, trapno, flags) != SWAP_SUCCESS) {
printk(KERN_ERR "MCE %#lx: cannot unmap page, give up\n", pfn);
res = -EBUSY;
goto out;
}
/*
* Torn down by someone else?
*/
if (PageLRU(p) && !PageSwapCache(p) && p->mapping == NULL) {
action_result(pfn, "already truncated LRU", IGNORED);
res = -EBUSY;
goto out;
}
res = -EBUSY;
for (ps = error_states;; ps++) {
if ((p->flags & ps->mask) == ps->res) {
res = page_action(ps, p, pfn);
break;
}
}
out:
unlock_page(hpage);
return res;
}
EXPORT_SYMBOL_GPL(memory_failure);
#define MEMORY_FAILURE_FIFO_ORDER 4
#define MEMORY_FAILURE_FIFO_SIZE (1 << MEMORY_FAILURE_FIFO_ORDER)
struct memory_failure_entry {
unsigned long pfn;
int trapno;
int flags;
};
struct memory_failure_cpu {
DECLARE_KFIFO(fifo, struct memory_failure_entry,
MEMORY_FAILURE_FIFO_SIZE);
spinlock_t lock;
struct work_struct work;
};
static DEFINE_PER_CPU(struct memory_failure_cpu, memory_failure_cpu);
/**
* memory_failure_queue - Schedule handling memory failure of a page.
* @pfn: Page Number of the corrupted page
* @trapno: Trap number reported in the signal to user space.
* @flags: Flags for memory failure handling
*
* This function is called by the low level hardware error handler
* when it detects hardware memory corruption of a page. It schedules
* the recovering of error page, including dropping pages, killing
* processes etc.
*
* The function is primarily of use for corruptions that
* happen outside the current execution context (e.g. when
* detected by a background scrubber)
*
* Can run in IRQ context.
*/
void memory_failure_queue(unsigned long pfn, int trapno, int flags)
{
struct memory_failure_cpu *mf_cpu;
unsigned long proc_flags;
struct memory_failure_entry entry = {
.pfn = pfn,
.trapno = trapno,
.flags = flags,
};
mf_cpu = &get_cpu_var(memory_failure_cpu);
spin_lock_irqsave(&mf_cpu->lock, proc_flags);
if (kfifo_put(&mf_cpu->fifo, &entry))
schedule_work_on(smp_processor_id(), &mf_cpu->work);
else
pr_err("Memory failure: buffer overflow when queuing memory failure at 0x%#lx\n",
pfn);
spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
put_cpu_var(memory_failure_cpu);
}
EXPORT_SYMBOL_GPL(memory_failure_queue);
static void memory_failure_work_func(struct work_struct *work)
{
struct memory_failure_cpu *mf_cpu;
struct memory_failure_entry entry = { 0, };
unsigned long proc_flags;
int gotten;
mf_cpu = &__get_cpu_var(memory_failure_cpu);
for (;;) {
spin_lock_irqsave(&mf_cpu->lock, proc_flags);
gotten = kfifo_get(&mf_cpu->fifo, &entry);
spin_unlock_irqrestore(&mf_cpu->lock, proc_flags);
if (!gotten)
break;
memory_failure(entry.pfn, entry.trapno, entry.flags);
}
}
static int __init memory_failure_init(void)
{
struct memory_failure_cpu *mf_cpu;
int cpu;
for_each_possible_cpu(cpu) {
mf_cpu = &per_cpu(memory_failure_cpu, cpu);
spin_lock_init(&mf_cpu->lock);
INIT_KFIFO(mf_cpu->fifo);
INIT_WORK(&mf_cpu->work, memory_failure_work_func);
}
return 0;
}
core_initcall(memory_failure_init);
/**
* unpoison_memory - Unpoison a previously poisoned page
* @pfn: Page number of the to be unpoisoned page
*
* Software-unpoison a page that has been poisoned by
* memory_failure() earlier.
*
* This is only done on the software-level, so it only works
* for linux injected failures, not real hardware failures
*
* Returns 0 for success, otherwise -errno.
*/
int unpoison_memory(unsigned long pfn)
{
struct page *page;
struct page *p;
int freeit = 0;
unsigned int nr_pages;
if (!pfn_valid(pfn))
return -ENXIO;
p = pfn_to_page(pfn);
page = compound_head(p);
if (!PageHWPoison(p)) {
pr_info("MCE: Page was already unpoisoned %#lx\n", pfn);
return 0;
}
nr_pages = 1 << compound_trans_order(page);
if (!get_page_unless_zero(page)) {
/*
* Since HWPoisoned hugepage should have non-zero refcount,
* race between memory failure and unpoison seems to happen.
* In such case unpoison fails and memory failure runs
* to the end.
*/
if (PageHuge(page)) {
pr_info("MCE: Memory failure is now running on free hugepage %#lx\n", pfn);
return 0;
}
if (TestClearPageHWPoison(p))
atomic_long_sub(nr_pages, &mce_bad_pages);
pr_info("MCE: Software-unpoisoned free page %#lx\n", pfn);
return 0;
}
lock_page(page);
/*
* This test is racy because PG_hwpoison is set outside of page lock.
* That's acceptable because that won't trigger kernel panic. Instead,
* the PG_hwpoison page will be caught and isolated on the entrance to
* the free buddy page pool.
*/
if (TestClearPageHWPoison(page)) {
pr_info("MCE: Software-unpoisoned page %#lx\n", pfn);
atomic_long_sub(nr_pages, &mce_bad_pages);
freeit = 1;
if (PageHuge(page))
clear_page_hwpoison_huge_page(page);
}
unlock_page(page);
put_page(page);
if (freeit)
put_page(page);
return 0;
}
EXPORT_SYMBOL(unpoison_memory);
static struct page *new_page(struct page *p, unsigned long private, int **x)
{
int nid = page_to_nid(p);
if (PageHuge(p))
return alloc_huge_page_node(page_hstate(compound_head(p)),
nid);
else
return alloc_pages_exact_node(nid, GFP_HIGHUSER_MOVABLE, 0);
}
/*
* Safely get reference count of an arbitrary page.
* Returns 0 for a free page, -EIO for a zero refcount page
* that is not free, and 1 for any other page type.
* For 1 the page is returned with increased page count, otherwise not.
*/
static int get_any_page(struct page *p, unsigned long pfn, int flags)
{
int ret;
if (flags & MF_COUNT_INCREASED)
return 1;
/*
* The lock_memory_hotplug prevents a race with memory hotplug.
* This is a big hammer, a better would be nicer.
*/
lock_memory_hotplug();
/*
* Isolate the page, so that it doesn't get reallocated if it
* was free.
*/
set_migratetype_isolate(p, true);
/*
* When the target page is a free hugepage, just remove it
* from free hugepage list.
*/
if (!get_page_unless_zero(compound_head(p))) {
if (PageHuge(p)) {
pr_info("%s: %#lx free huge page\n", __func__, pfn);
ret = dequeue_hwpoisoned_huge_page(compound_head(p));
} else if (is_free_buddy_page(p)) {
pr_info("%s: %#lx free buddy page\n", __func__, pfn);
/* Set hwpoison bit while page is still isolated */
SetPageHWPoison(p);
ret = 0;
} else {
pr_info("%s: %#lx: unknown zero refcount page type %lx\n",
__func__, pfn, p->flags);
ret = -EIO;
}
} else {
/* Not a free page */
ret = 1;
}
unset_migratetype_isolate(p, MIGRATE_MOVABLE);
unlock_memory_hotplug();
return ret;
}
static int soft_offline_huge_page(struct page *page, int flags)
{
int ret;
unsigned long pfn = page_to_pfn(page);
struct page *hpage = compound_head(page);
ret = get_any_page(page, pfn, flags);
if (ret < 0)
return ret;
if (ret == 0)
goto done;
if (PageHWPoison(hpage)) {
put_page(hpage);
pr_info("soft offline: %#lx hugepage already poisoned\n", pfn);
return -EBUSY;
}
/* Keep page count to indicate a given hugepage is isolated. */
ret = migrate_huge_page(hpage, new_page, MPOL_MF_MOVE_ALL, false,
MIGRATE_SYNC);
put_page(hpage);
if (ret) {
pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
pfn, ret, page->flags);
return ret;
}
done:
if (!PageHWPoison(hpage))
atomic_long_add(1 << compound_trans_order(hpage),
&mce_bad_pages);
set_page_hwpoison_huge_page(hpage);
dequeue_hwpoisoned_huge_page(hpage);
/* keep elevated page count for bad page */
return ret;
}
/**
* soft_offline_page - Soft offline a page.
* @page: page to offline
* @flags: flags. Same as memory_failure().
*
* Returns 0 on success, otherwise negated errno.
*
* Soft offline a page, by migration or invalidation,
* without killing anything. This is for the case when
* a page is not corrupted yet (so it's still valid to access),
* but has had a number of corrected errors and is better taken
* out.
*
* The actual policy on when to do that is maintained by
* user space.
*
* This should never impact any application or cause data loss,
* however it might take some time.
*
* This is not a 100% solution for all memory, but tries to be
* ``good enough'' for the majority of memory.
*/
int soft_offline_page(struct page *page, int flags)
{
int ret;
unsigned long pfn = page_to_pfn(page);
struct page *hpage = compound_trans_head(page);
if (PageHuge(page))
return soft_offline_huge_page(page, flags);
if (PageTransHuge(hpage)) {
if (PageAnon(hpage) && unlikely(split_huge_page(hpage))) {
pr_info("soft offline: %#lx: failed to split THP\n",
pfn);
return -EBUSY;
}
}
ret = get_any_page(page, pfn, flags);
if (ret < 0)
return ret;
if (ret == 0)
goto done;
/*
* Page cache page we can handle?
*/
if (!PageLRU(page)) {
/*
* Try to free it.
*/
put_page(page);
shake_page(page, 1);
/*
* Did it turn free?
*/
ret = get_any_page(page, pfn, 0);
if (ret < 0)
return ret;
if (ret == 0)
goto done;
}
if (!PageLRU(page)) {
pr_info("soft_offline: %#lx: unknown non LRU page type %lx\n",
pfn, page->flags);
return -EIO;
}
lock_page(page);
wait_on_page_writeback(page);
/*
* Synchronized using the page lock with memory_failure()
*/
if (PageHWPoison(page)) {
unlock_page(page);
put_page(page);
pr_info("soft offline: %#lx page already poisoned\n", pfn);
return -EBUSY;
}
/*
* Try to invalidate first. This should work for
* non dirty unmapped page cache pages.
*/
ret = invalidate_inode_page(page);
unlock_page(page);
/*
* RED-PEN would be better to keep it isolated here, but we
* would need to fix isolation locking first.
*/
if (ret == 1) {
put_page(page);
ret = 0;
pr_info("soft_offline: %#lx: invalidated\n", pfn);
goto done;
}
/*
* Simple invalidation didn't work.
* Try to migrate to a new page instead. migrate.c
* handles a large number of cases for us.
*/
ret = isolate_lru_page(page);
/*
* Drop page reference which is came from get_any_page()
* successful isolate_lru_page() already took another one.
*/
put_page(page);
if (!ret) {
LIST_HEAD(pagelist);
inc_zone_page_state(page, NR_ISOLATED_ANON +
page_is_file_cache(page));
list_add(&page->lru, &pagelist);
ret = migrate_pages(&pagelist, new_page, MPOL_MF_MOVE_ALL,
false, MIGRATE_SYNC,
MR_MEMORY_FAILURE);
if (ret) {
putback_lru_pages(&pagelist);
pr_info("soft offline: %#lx: migration failed %d, type %lx\n",
pfn, ret, page->flags);
if (ret > 0)
ret = -EIO;
}
} else {
pr_info("soft offline: %#lx: isolation failed: %d, page count %d, type %lx\n",
pfn, ret, page_count(page), page->flags);
}
if (ret)
return ret;
done:
atomic_long_add(1, &mce_bad_pages);
SetPageHWPoison(page);
/* keep elevated page count for bad page */
return ret;
}