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authorShaohua Li <shaohua.li@intel.com>2010-08-09 17:19:06 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2010-08-09 20:44:58 -0700
commitff36b801624d02a876bb7deded6ab860ea3503f2 (patch)
treea3f44d01de629234d70ad6211b9fd73fd705a76c
parent7e496299d4d2ad8083effed6c5a18313a919edc6 (diff)
downloadop-kernel-dev-ff36b801624d02a876bb7deded6ab860ea3503f2.zip
op-kernel-dev-ff36b801624d02a876bb7deded6ab860ea3503f2.tar.gz
shmem: reduce pagefault lock contention
I'm running a shmem pagefault test case (see attached file) under a 64 CPU system. Profile shows shmem_inode_info->lock is heavily contented and 100% CPUs time are trying to get the lock. In the pagefault (no swap) case, shmem_getpage gets the lock twice, the last one is avoidable if we prealloc a page so we could reduce one time of locking. This is what below patch does. The result of the test case: 2.6.35-rc3: ~20s 2.6.35-rc3 + patch: ~12s so this is 40% improvement. One might argue if we could have better locking for shmem. But even shmem is lockless, the pagefault will soon have pagecache lock heavily contented because shmem must add new page to pagecache. So before we have better locking for pagecache, improving shmem locking doesn't have too much improvement. I did a similar pagefault test against a ramfs file, the test result is ~10.5s. [akpm@linux-foundation.org: fix comment, clean up code layout, elimintate code duplication] Signed-off-by: Shaohua Li <shaohua.li@intel.com> Cc: Hugh Dickins <hughd@google.com> Cc: "Zhang, Yanmin" <yanmin.zhang@intel.com> Cc: Tim Chen <tim.c.chen@linux.intel.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/shmem.c70
1 files changed, 49 insertions, 21 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 0618fda..566f9a4 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1222,6 +1222,7 @@ static int shmem_getpage(struct inode *inode, unsigned long idx,
struct shmem_sb_info *sbinfo;
struct page *filepage = *pagep;
struct page *swappage;
+ struct page *prealloc_page = NULL;
swp_entry_t *entry;
swp_entry_t swap;
gfp_t gfp;
@@ -1246,7 +1247,6 @@ repeat:
filepage = find_lock_page(mapping, idx);
if (filepage && PageUptodate(filepage))
goto done;
- error = 0;
gfp = mapping_gfp_mask(mapping);
if (!filepage) {
/*
@@ -1257,7 +1257,19 @@ repeat:
if (error)
goto failed;
radix_tree_preload_end();
+ if (sgp != SGP_READ && !prealloc_page) {
+ /* We don't care if this fails */
+ prealloc_page = shmem_alloc_page(gfp, info, idx);
+ if (prealloc_page) {
+ if (mem_cgroup_cache_charge(prealloc_page,
+ current->mm, GFP_KERNEL)) {
+ page_cache_release(prealloc_page);
+ prealloc_page = NULL;
+ }
+ }
+ }
}
+ error = 0;
spin_lock(&info->lock);
shmem_recalc_inode(inode);
@@ -1405,28 +1417,38 @@ repeat:
if (!filepage) {
int ret;
- spin_unlock(&info->lock);
- filepage = shmem_alloc_page(gfp, info, idx);
- if (!filepage) {
- shmem_unacct_blocks(info->flags, 1);
- shmem_free_blocks(inode, 1);
- error = -ENOMEM;
- goto failed;
- }
- SetPageSwapBacked(filepage);
+ if (!prealloc_page) {
+ spin_unlock(&info->lock);
+ filepage = shmem_alloc_page(gfp, info, idx);
+ if (!filepage) {
+ shmem_unacct_blocks(info->flags, 1);
+ shmem_free_blocks(inode, 1);
+ error = -ENOMEM;
+ goto failed;
+ }
+ SetPageSwapBacked(filepage);
- /* Precharge page while we can wait, compensate after */
- error = mem_cgroup_cache_charge(filepage, current->mm,
- GFP_KERNEL);
- if (error) {
- page_cache_release(filepage);
- shmem_unacct_blocks(info->flags, 1);
- shmem_free_blocks(inode, 1);
- filepage = NULL;
- goto failed;
+ /*
+ * Precharge page while we can wait, compensate
+ * after
+ */
+ error = mem_cgroup_cache_charge(filepage,
+ current->mm, GFP_KERNEL);
+ if (error) {
+ page_cache_release(filepage);
+ shmem_unacct_blocks(info->flags, 1);
+ shmem_free_blocks(inode, 1);
+ filepage = NULL;
+ goto failed;
+ }
+
+ spin_lock(&info->lock);
+ } else {
+ filepage = prealloc_page;
+ prealloc_page = NULL;
+ SetPageSwapBacked(filepage);
}
- spin_lock(&info->lock);
entry = shmem_swp_alloc(info, idx, sgp);
if (IS_ERR(entry))
error = PTR_ERR(entry);
@@ -1467,13 +1489,19 @@ repeat:
}
done:
*pagep = filepage;
- return 0;
+ error = 0;
+ goto out;
failed:
if (*pagep != filepage) {
unlock_page(filepage);
page_cache_release(filepage);
}
+out:
+ if (prealloc_page) {
+ mem_cgroup_uncharge_cache_page(prealloc_page);
+ page_cache_release(prealloc_page);
+ }
return error;
}
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