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mm: frontswap: core frontswap functionality

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This patch, 3of4, provides the core frontswap code that interfaces between
the hooks in the swap subsystem and a frontswap backend via frontswap_ops.

---
New file added: mm/frontswap.c

[v14: add support for writethrough, per suggestion by aarcange@redhat.com]
[v11: sjenning@linux.vnet.ibm.com: s/puts/failed_puts/]
[v10: sjenning@linux.vnet.ibm.com: fix debugfs calls on 32-bit]
[v9: akpm@linux-foundation.org: change "flush" to "invalidate", part 1]
[v9: akpm@linux-foundation.org: mark some statics __read_mostly]
[v9: akpm@linux-foundation.org: add clarifying comments]
[v9: akpm@linux-foundation.org: no need to loop repeating try_to_unuse]
[v9: error27@gmail.com: remove superfluous check for NULL]
[v8: rebase to 3.0-rc4]
[v8: kamezawa.hiroyu@jp.fujitsu.com: add comment to clarify find_next_to_unuse]
[v7: rebase to 3.0-rc3]
[v7: JBeulich@novell.com: use new static inlines, no-ops if not config'd]
[v6: rebase to 3.1-rc1]
[v6: lliubbo@gmail.com: use vzalloc]
[v6: lliubbo@gmail.com: fix null pointer deref if vzalloc fails]
[v6: konrad.wilk@oracl.com: various checks and code clarifications/comments]
[v4: rebase to 2.6.39]
Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Acked-by: Jan Beulich <JBeulich@novell.com>
Acked-by: Seth Jennings <sjenning@linux.vnet.ibm.com>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Matthew Wilcox <matthew@wil.cx>
Cc: Chris Mason <chris.mason@oracle.com>
Cc: Rik Riel <riel@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
[v12: Squashed s/flush/invalidate/ in]
[v15: A bit of cleanup and seperate DEBUGFS]
Signed-off-by: Konrad Wilk <konrad.wilk@oracle.com>
This commit is contained in:
Dan Magenheimer 2012-04-09 17:09:27 -06:00 committed by Konrad Rzeszutek Wilk
parent 38b5faf4b1
commit 29f233cfff
1 changed files with 314 additions and 0 deletions
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mm/frontswap.c Normal file
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/*
* Frontswap frontend
*
* This code provides the generic "frontend" layer to call a matching
* "backend" driver implementation of frontswap. See
* Documentation/vm/frontswap.txt for more information.
*
* Copyright (C) 2009-2012 Oracle Corp. All rights reserved.
* Author: Dan Magenheimer
*
* This work is licensed under the terms of the GNU GPL, version 2.
*/
#include <linux/mm.h>
#include <linux/mman.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/proc_fs.h>
#include <linux/security.h>
#include <linux/capability.h>
#include <linux/module.h>
#include <linux/uaccess.h>
#include <linux/debugfs.h>
#include <linux/frontswap.h>
#include <linux/swapfile.h>
/*
* frontswap_ops is set by frontswap_register_ops to contain the pointers
* to the frontswap "backend" implementation functions.
*/
static struct frontswap_ops frontswap_ops __read_mostly;
/*
* This global enablement flag reduces overhead on systems where frontswap_ops
* has not been registered, so is preferred to the slower alternative: a
* function call that checks a non-global.
*/
bool frontswap_enabled __read_mostly;
EXPORT_SYMBOL(frontswap_enabled);
/*
* If enabled, frontswap_put will return failure even on success. As
* a result, the swap subsystem will always write the page to swap, in
* effect converting frontswap into a writethrough cache. In this mode,
* there is no direct reduction in swap writes, but a frontswap backend
* can unilaterally "reclaim" any pages in use with no data loss, thus
* providing increases control over maximum memory usage due to frontswap.
*/
static bool frontswap_writethrough_enabled __read_mostly;
#ifdef CONFIG_DEBUG_FS
/*
* Counters available via /sys/kernel/debug/frontswap (if debugfs is
* properly configured). These are for information only so are not protected
* against increment races.
*/
static u64 frontswap_gets;
static u64 frontswap_succ_puts;
static u64 frontswap_failed_puts;
static u64 frontswap_invalidates;
static inline void inc_frontswap_gets(void) {
frontswap_gets++;
}
static inline void inc_frontswap_succ_puts(void) {
frontswap_succ_puts++;
}
static inline void inc_frontswap_failed_puts(void) {
frontswap_failed_puts++;
}
static inline void inc_frontswap_invalidates(void) {
frontswap_invalidates++;
}
#else
static inline void inc_frontswap_gets(void) { }
static inline void inc_frontswap_succ_puts(void) { }
static inline void inc_frontswap_failed_puts(void) { }
static inline void inc_frontswap_invalidates(void) { }
#endif
/*
* Register operations for frontswap, returning previous thus allowing
* detection of multiple backends and possible nesting.
*/
struct frontswap_ops frontswap_register_ops(struct frontswap_ops *ops)
{
struct frontswap_ops old = frontswap_ops;
frontswap_ops = *ops;
frontswap_enabled = true;
return old;
}
EXPORT_SYMBOL(frontswap_register_ops);
/*
* Enable/disable frontswap writethrough (see above).
*/
void frontswap_writethrough(bool enable)
{
frontswap_writethrough_enabled = enable;
}
EXPORT_SYMBOL(frontswap_writethrough);
/*
* Called when a swap device is swapon'd.
*/
void __frontswap_init(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
BUG_ON(sis == NULL);
if (sis->frontswap_map == NULL)
return;
if (frontswap_enabled)
(*frontswap_ops.init)(type);
}
EXPORT_SYMBOL(__frontswap_init);
/*
* "Put" data from a page to frontswap and associate it with the page's
* swaptype and offset. Page must be locked and in the swap cache.
* If frontswap already contains a page with matching swaptype and
* offset, the frontswap implmentation may either overwrite the data and
* return success or invalidate the page from frontswap and return failure.
*/
int __frontswap_put_page(struct page *page)
{
int ret = -1, dup = 0;
swp_entry_t entry = { .val = page_private(page), };
int type = swp_type(entry);
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
dup = 1;
ret = (*frontswap_ops.put_page)(type, offset, page);
if (ret == 0) {
frontswap_set(sis, offset);
inc_frontswap_succ_puts();
if (!dup)
atomic_inc(&sis->frontswap_pages);
} else if (dup) {
/*
failed dup always results in automatic invalidate of
the (older) page from frontswap
*/
frontswap_clear(sis, offset);
atomic_dec(&sis->frontswap_pages);
inc_frontswap_failed_puts();
} else
inc_frontswap_failed_puts();
if (frontswap_writethrough_enabled)
/* report failure so swap also writes to swap device */
ret = -1;
return ret;
}
EXPORT_SYMBOL(__frontswap_put_page);
/*
* "Get" data from frontswap associated with swaptype and offset that were
* specified when the data was put to frontswap and use it to fill the
* specified page with data. Page must be locked and in the swap cache.
*/
int __frontswap_get_page(struct page *page)
{
int ret = -1;
swp_entry_t entry = { .val = page_private(page), };
int type = swp_type(entry);
struct swap_info_struct *sis = swap_info[type];
pgoff_t offset = swp_offset(entry);
BUG_ON(!PageLocked(page));
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset))
ret = (*frontswap_ops.get_page)(type, offset, page);
if (ret == 0)
inc_frontswap_gets();
return ret;
}
EXPORT_SYMBOL(__frontswap_get_page);
/*
* Invalidate any data from frontswap associated with the specified swaptype
* and offset so that a subsequent "get" will fail.
*/
void __frontswap_invalidate_page(unsigned type, pgoff_t offset)
{
struct swap_info_struct *sis = swap_info[type];
BUG_ON(sis == NULL);
if (frontswap_test(sis, offset)) {
(*frontswap_ops.invalidate_page)(type, offset);
atomic_dec(&sis->frontswap_pages);
frontswap_clear(sis, offset);
inc_frontswap_invalidates();
}
}
EXPORT_SYMBOL(__frontswap_invalidate_page);
/*
* Invalidate all data from frontswap associated with all offsets for the
* specified swaptype.
*/
void __frontswap_invalidate_area(unsigned type)
{
struct swap_info_struct *sis = swap_info[type];
BUG_ON(sis == NULL);
if (sis->frontswap_map == NULL)
return;
(*frontswap_ops.invalidate_area)(type);
atomic_set(&sis->frontswap_pages, 0);
memset(sis->frontswap_map, 0, sis->max / sizeof(long));
}
EXPORT_SYMBOL(__frontswap_invalidate_area);
/*
* Frontswap, like a true swap device, may unnecessarily retain pages
* under certain circumstances; "shrink" frontswap is essentially a
* "partial swapoff" and works by calling try_to_unuse to attempt to
* unuse enough frontswap pages to attempt to -- subject to memory
* constraints -- reduce the number of pages in frontswap to the
* number given in the parameter target_pages.
*/
void frontswap_shrink(unsigned long target_pages)
{
struct swap_info_struct *si = NULL;
int si_frontswap_pages;
unsigned long total_pages = 0, total_pages_to_unuse;
unsigned long pages = 0, pages_to_unuse = 0;
int type;
bool locked = false;
/*
* we don't want to hold swap_lock while doing a very
* lengthy try_to_unuse, but swap_list may change
* so restart scan from swap_list.head each time
*/
spin_lock(&swap_lock);
locked = true;
total_pages = 0;
for (type = swap_list.head; type >= 0; type = si->next) {
si = swap_info[type];
total_pages += atomic_read(&si->frontswap_pages);
}
if (total_pages <= target_pages)
goto out;
total_pages_to_unuse = total_pages - target_pages;
for (type = swap_list.head; type >= 0; type = si->next) {
si = swap_info[type];
si_frontswap_pages = atomic_read(&si->frontswap_pages);
if (total_pages_to_unuse < si_frontswap_pages)
pages = pages_to_unuse = total_pages_to_unuse;
else {
pages = si_frontswap_pages;
pages_to_unuse = 0; /* unuse all */
}
/* ensure there is enough RAM to fetch pages from frontswap */
if (security_vm_enough_memory_mm(current->mm, pages))
continue;
vm_unacct_memory(pages);
break;
}
if (type < 0)
goto out;
locked = false;
spin_unlock(&swap_lock);
try_to_unuse(type, true, pages_to_unuse);
out:
if (locked)
spin_unlock(&swap_lock);
return;
}
EXPORT_SYMBOL(frontswap_shrink);
/*
* Count and return the number of frontswap pages across all
* swap devices. This is exported so that backend drivers can
* determine current usage without reading debugfs.
*/
unsigned long frontswap_curr_pages(void)
{
int type;
unsigned long totalpages = 0;
struct swap_info_struct *si = NULL;
spin_lock(&swap_lock);
for (type = swap_list.head; type >= 0; type = si->next) {
si = swap_info[type];
totalpages += atomic_read(&si->frontswap_pages);
}
spin_unlock(&swap_lock);
return totalpages;
}
EXPORT_SYMBOL(frontswap_curr_pages);
static int __init init_frontswap(void)
{
#ifdef CONFIG_DEBUG_FS
struct dentry *root = debugfs_create_dir("frontswap", NULL);
if (root == NULL)
return -ENXIO;
debugfs_create_u64("gets", S_IRUGO, root, &frontswap_gets);
debugfs_create_u64("succ_puts", S_IRUGO, root, &frontswap_succ_puts);
debugfs_create_u64("failed_puts", S_IRUGO, root,
&frontswap_failed_puts);
debugfs_create_u64("invalidates", S_IRUGO,
root, &frontswap_invalidates);
#endif
return 0;
}
module_init(init_frontswap);