mirror of
https://github.com/torvalds/linux.git
synced 2024-11-10 22:21:40 +00:00
b4ed71f557
The naming of pgtable_page_{ctor,dtor}() seems to have confused a few
people, and until recently arm64 used these erroneously/pointlessly for
other levels of page table.
To make it incredibly clear that these only apply to the PTE level, and to
align with the naming of pgtable_pmd_page_{ctor,dtor}(), let's rename them
to pgtable_pte_page_{ctor,dtor}().
These changes were generated with the following shell script:
----
git grep -lw 'pgtable_page_.tor' | while read FILE; do
sed -i '{s/pgtable_page_ctor/pgtable_pte_page_ctor/}' $FILE;
sed -i '{s/pgtable_page_dtor/pgtable_pte_page_dtor/}' $FILE;
done
----
... with the documentation re-flowed to remain under 80 columns, and
whitespace fixed up in macros to keep backslashes aligned.
There should be no functional change as a result of this patch.
Link: http://lkml.kernel.org/r/20190722141133.3116-1-mark.rutland@arm.com
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org> [m68k]
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
101 lines
3.6 KiB
ReStructuredText
101 lines
3.6 KiB
ReStructuredText
.. _split_page_table_lock:
|
|
|
|
=====================
|
|
Split page table lock
|
|
=====================
|
|
|
|
Originally, mm->page_table_lock spinlock protected all page tables of the
|
|
mm_struct. But this approach leads to poor page fault scalability of
|
|
multi-threaded applications due high contention on the lock. To improve
|
|
scalability, split page table lock was introduced.
|
|
|
|
With split page table lock we have separate per-table lock to serialize
|
|
access to the table. At the moment we use split lock for PTE and PMD
|
|
tables. Access to higher level tables protected by mm->page_table_lock.
|
|
|
|
There are helpers to lock/unlock a table and other accessor functions:
|
|
|
|
- pte_offset_map_lock()
|
|
maps pte and takes PTE table lock, returns pointer to the taken
|
|
lock;
|
|
- pte_unmap_unlock()
|
|
unlocks and unmaps PTE table;
|
|
- pte_alloc_map_lock()
|
|
allocates PTE table if needed and take the lock, returns pointer
|
|
to taken lock or NULL if allocation failed;
|
|
- pte_lockptr()
|
|
returns pointer to PTE table lock;
|
|
- pmd_lock()
|
|
takes PMD table lock, returns pointer to taken lock;
|
|
- pmd_lockptr()
|
|
returns pointer to PMD table lock;
|
|
|
|
Split page table lock for PTE tables is enabled compile-time if
|
|
CONFIG_SPLIT_PTLOCK_CPUS (usually 4) is less or equal to NR_CPUS.
|
|
If split lock is disabled, all tables guaded by mm->page_table_lock.
|
|
|
|
Split page table lock for PMD tables is enabled, if it's enabled for PTE
|
|
tables and the architecture supports it (see below).
|
|
|
|
Hugetlb and split page table lock
|
|
=================================
|
|
|
|
Hugetlb can support several page sizes. We use split lock only for PMD
|
|
level, but not for PUD.
|
|
|
|
Hugetlb-specific helpers:
|
|
|
|
- huge_pte_lock()
|
|
takes pmd split lock for PMD_SIZE page, mm->page_table_lock
|
|
otherwise;
|
|
- huge_pte_lockptr()
|
|
returns pointer to table lock;
|
|
|
|
Support of split page table lock by an architecture
|
|
===================================================
|
|
|
|
There's no need in special enabling of PTE split page table lock: everything
|
|
required is done by pgtable_pte_page_ctor() and pgtable_pte_page_dtor(), which
|
|
must be called on PTE table allocation / freeing.
|
|
|
|
Make sure the architecture doesn't use slab allocator for page table
|
|
allocation: slab uses page->slab_cache for its pages.
|
|
This field shares storage with page->ptl.
|
|
|
|
PMD split lock only makes sense if you have more than two page table
|
|
levels.
|
|
|
|
PMD split lock enabling requires pgtable_pmd_page_ctor() call on PMD table
|
|
allocation and pgtable_pmd_page_dtor() on freeing.
|
|
|
|
Allocation usually happens in pmd_alloc_one(), freeing in pmd_free() and
|
|
pmd_free_tlb(), but make sure you cover all PMD table allocation / freeing
|
|
paths: i.e X86_PAE preallocate few PMDs on pgd_alloc().
|
|
|
|
With everything in place you can set CONFIG_ARCH_ENABLE_SPLIT_PMD_PTLOCK.
|
|
|
|
NOTE: pgtable_pte_page_ctor() and pgtable_pmd_page_ctor() can fail -- it must
|
|
be handled properly.
|
|
|
|
page->ptl
|
|
=========
|
|
|
|
page->ptl is used to access split page table lock, where 'page' is struct
|
|
page of page containing the table. It shares storage with page->private
|
|
(and few other fields in union).
|
|
|
|
To avoid increasing size of struct page and have best performance, we use a
|
|
trick:
|
|
|
|
- if spinlock_t fits into long, we use page->ptr as spinlock, so we
|
|
can avoid indirect access and save a cache line.
|
|
- if size of spinlock_t is bigger then size of long, we use page->ptl as
|
|
pointer to spinlock_t and allocate it dynamically. This allows to use
|
|
split lock with enabled DEBUG_SPINLOCK or DEBUG_LOCK_ALLOC, but costs
|
|
one more cache line for indirect access;
|
|
|
|
The spinlock_t allocated in pgtable_pte_page_ctor() for PTE table and in
|
|
pgtable_pmd_page_ctor() for PMD table.
|
|
|
|
Please, never access page->ptl directly -- use appropriate helper.
|