diff options
author | Hugh Dickins <hugh@veritas.com> | 2005-10-29 18:16:40 -0700 |
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committer | Linus Torvalds <torvalds@g5.osdl.org> | 2005-10-29 21:40:42 -0700 |
commit | 4c21e2f2441dc5fbb957b030333f5a3f2d02dea7 (patch) | |
tree | 1f76d33bb1d76221c6424bc5fed080a4f91349a6 /mm/shmem.c | |
parent | b38c6845b695141259019e2b7c0fe6c32a6e720d (diff) | |
download | linux-4c21e2f2441dc5fbb957b030333f5a3f2d02dea7.tar.gz linux-4c21e2f2441dc5fbb957b030333f5a3f2d02dea7.tar.xz |
[PATCH] mm: split page table lock
Christoph Lameter demonstrated very poor scalability on the SGI 512-way, with
a many-threaded application which concurrently initializes different parts of
a large anonymous area.
This patch corrects that, by using a separate spinlock per page table page, to
guard the page table entries in that page, instead of using the mm's single
page_table_lock. (But even then, page_table_lock is still used to guard page
table allocation, and anon_vma allocation.)
In this implementation, the spinlock is tucked inside the struct page of the
page table page: with a BUILD_BUG_ON in case it overflows - which it would in
the case of 32-bit PA-RISC with spinlock debugging enabled.
Splitting the lock is not quite for free: another cacheline access. Ideally,
I suppose we would use split ptlock only for multi-threaded processes on
multi-cpu machines; but deciding that dynamically would have its own costs.
So for now enable it by config, at some number of cpus - since the Kconfig
language doesn't support inequalities, let preprocessor compare that with
NR_CPUS. But I don't think it's worth being user-configurable: for good
testing of both split and unsplit configs, split now at 4 cpus, and perhaps
change that to 8 later.
There is a benefit even for singly threaded processes: kswapd can be attacking
one part of the mm while another part is busy faulting.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r-- | mm/shmem.c | 22 |
1 files changed, 10 insertions, 12 deletions
diff --git a/mm/shmem.c b/mm/shmem.c index 37777f4c11f8..dc25565a61e9 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -71,9 +71,6 @@ /* Pretend that each entry is of this size in directory's i_size */ #define BOGO_DIRENT_SIZE 20 -/* Keep swapped page count in private field of indirect struct page */ -#define nr_swapped private - /* Flag allocation requirements to shmem_getpage and shmem_swp_alloc */ enum sgp_type { SGP_QUICK, /* don't try more than file page cache lookup */ @@ -324,8 +321,10 @@ static void shmem_swp_set(struct shmem_inode_info *info, swp_entry_t *entry, uns entry->val = value; info->swapped += incdec; - if ((unsigned long)(entry - info->i_direct) >= SHMEM_NR_DIRECT) - kmap_atomic_to_page(entry)->nr_swapped += incdec; + if ((unsigned long)(entry - info->i_direct) >= SHMEM_NR_DIRECT) { + struct page *page = kmap_atomic_to_page(entry); + set_page_private(page, page_private(page) + incdec); + } } /* @@ -368,9 +367,8 @@ static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long spin_unlock(&info->lock); page = shmem_dir_alloc(mapping_gfp_mask(inode->i_mapping) | __GFP_ZERO); - if (page) { - page->nr_swapped = 0; - } + if (page) + set_page_private(page, 0); spin_lock(&info->lock); if (!page) { @@ -561,7 +559,7 @@ static void shmem_truncate(struct inode *inode) diroff = 0; } subdir = dir[diroff]; - if (subdir && subdir->nr_swapped) { + if (subdir && page_private(subdir)) { size = limit - idx; if (size > ENTRIES_PER_PAGE) size = ENTRIES_PER_PAGE; @@ -572,10 +570,10 @@ static void shmem_truncate(struct inode *inode) nr_swaps_freed += freed; if (offset) spin_lock(&info->lock); - subdir->nr_swapped -= freed; + set_page_private(subdir, page_private(subdir) - freed); if (offset) spin_unlock(&info->lock); - BUG_ON(subdir->nr_swapped > offset); + BUG_ON(page_private(subdir) > offset); } if (offset) offset = 0; @@ -743,7 +741,7 @@ static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, s dir = shmem_dir_map(subdir); } subdir = *dir; - if (subdir && subdir->nr_swapped) { + if (subdir && page_private(subdir)) { ptr = shmem_swp_map(subdir); size = limit - idx; if (size > ENTRIES_PER_PAGE) |