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authorJohannes Weiner <hannes@cmpxchg.org>2014-08-08 14:19:20 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2014-08-08 15:57:17 -0700
commit00501b531c4723972aa11d6d4ebcf8d6552007c8 (patch)
treeb3ad4850d58f137cf87b8424412d962fb251839f /mm/shmem.c
parent4449a51a7c281602d3a385044ab928322a122a02 (diff)
downloadlinux-00501b531c4723972aa11d6d4ebcf8d6552007c8.tar.bz2
mm: memcontrol: rewrite charge API
These patches rework memcg charge lifetime to integrate more naturally with the lifetime of user pages. This drastically simplifies the code and reduces charging and uncharging overhead. The most expensive part of charging and uncharging is the page_cgroup bit spinlock, which is removed entirely after this series. Here are the top-10 profile entries of a stress test that reads a 128G sparse file on a freshly booted box, without even a dedicated cgroup (i.e. executing in the root memcg). Before: 15.36% cat [kernel.kallsyms] [k] copy_user_generic_string 13.31% cat [kernel.kallsyms] [k] memset 11.48% cat [kernel.kallsyms] [k] do_mpage_readpage 4.23% cat [kernel.kallsyms] [k] get_page_from_freelist 2.38% cat [kernel.kallsyms] [k] put_page 2.32% cat [kernel.kallsyms] [k] __mem_cgroup_commit_charge 2.18% kswapd0 [kernel.kallsyms] [k] __mem_cgroup_uncharge_common 1.92% kswapd0 [kernel.kallsyms] [k] shrink_page_list 1.86% cat [kernel.kallsyms] [k] __radix_tree_lookup 1.62% cat [kernel.kallsyms] [k] __pagevec_lru_add_fn After: 15.67% cat [kernel.kallsyms] [k] copy_user_generic_string 13.48% cat [kernel.kallsyms] [k] memset 11.42% cat [kernel.kallsyms] [k] do_mpage_readpage 3.98% cat [kernel.kallsyms] [k] get_page_from_freelist 2.46% cat [kernel.kallsyms] [k] put_page 2.13% kswapd0 [kernel.kallsyms] [k] shrink_page_list 1.88% cat [kernel.kallsyms] [k] __radix_tree_lookup 1.67% cat [kernel.kallsyms] [k] __pagevec_lru_add_fn 1.39% kswapd0 [kernel.kallsyms] [k] free_pcppages_bulk 1.30% cat [kernel.kallsyms] [k] kfree As you can see, the memcg footprint has shrunk quite a bit. text data bss dec hex filename 37970 9892 400 48262 bc86 mm/memcontrol.o.old 35239 9892 400 45531 b1db mm/memcontrol.o This patch (of 4): The memcg charge API charges pages before they are rmapped - i.e. have an actual "type" - and so every callsite needs its own set of charge and uncharge functions to know what type is being operated on. Worse, uncharge has to happen from a context that is still type-specific, rather than at the end of the page's lifetime with exclusive access, and so requires a lot of synchronization. Rewrite the charge API to provide a generic set of try_charge(), commit_charge() and cancel_charge() transaction operations, much like what's currently done for swap-in: mem_cgroup_try_charge() attempts to reserve a charge, reclaiming pages from the memcg if necessary. mem_cgroup_commit_charge() commits the page to the charge once it has a valid page->mapping and PageAnon() reliably tells the type. mem_cgroup_cancel_charge() aborts the transaction. This reduces the charge API and enables subsequent patches to drastically simplify uncharging. As pages need to be committed after rmap is established but before they are added to the LRU, page_add_new_anon_rmap() must stop doing LRU additions again. Revive lru_cache_add_active_or_unevictable(). [hughd@google.com: fix shmem_unuse] [hughd@google.com: Add comments on the private use of -EAGAIN] Signed-off-by: Johannes Weiner <hannes@cmpxchg.org> Acked-by: Michal Hocko <mhocko@suse.cz> Cc: Tejun Heo <tj@kernel.org> Cc: Vladimir Davydov <vdavydov@parallels.com> Signed-off-by: Hugh Dickins <hughd@google.com> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/shmem.c')
-rw-r--r--mm/shmem.c37
1 files changed, 23 insertions, 14 deletions
diff --git a/mm/shmem.c b/mm/shmem.c
index 302d1cf7ad07..1f1a8085538b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -621,7 +621,7 @@ static int shmem_unuse_inode(struct shmem_inode_info *info,
radswap = swp_to_radix_entry(swap);
index = radix_tree_locate_item(&mapping->page_tree, radswap);
if (index == -1)
- return 0;
+ return -EAGAIN; /* tell shmem_unuse we found nothing */
/*
* Move _head_ to start search for next from here.
@@ -680,7 +680,6 @@ static int shmem_unuse_inode(struct shmem_inode_info *info,
spin_unlock(&info->lock);
swap_free(swap);
}
- error = 1; /* not an error, but entry was found */
}
return error;
}
@@ -692,7 +691,7 @@ int shmem_unuse(swp_entry_t swap, struct page *page)
{
struct list_head *this, *next;
struct shmem_inode_info *info;
- int found = 0;
+ struct mem_cgroup *memcg;
int error = 0;
/*
@@ -707,26 +706,32 @@ int shmem_unuse(swp_entry_t swap, struct page *page)
* the shmem_swaplist_mutex which might hold up shmem_writepage().
* Charged back to the user (not to caller) when swap account is used.
*/
- error = mem_cgroup_charge_file(page, current->mm, GFP_KERNEL);
+ error = mem_cgroup_try_charge(page, current->mm, GFP_KERNEL, &memcg);
if (error)
goto out;
/* No radix_tree_preload: swap entry keeps a place for page in tree */
+ error = -EAGAIN;
mutex_lock(&shmem_swaplist_mutex);
list_for_each_safe(this, next, &shmem_swaplist) {
info = list_entry(this, struct shmem_inode_info, swaplist);
if (info->swapped)
- found = shmem_unuse_inode(info, swap, &page);
+ error = shmem_unuse_inode(info, swap, &page);
else
list_del_init(&info->swaplist);
cond_resched();
- if (found)
+ if (error != -EAGAIN)
break;
+ /* found nothing in this: move on to search the next */
}
mutex_unlock(&shmem_swaplist_mutex);
- if (found < 0)
- error = found;
+ if (error) {
+ if (error != -ENOMEM)
+ error = 0;
+ mem_cgroup_cancel_charge(page, memcg);
+ } else
+ mem_cgroup_commit_charge(page, memcg, true);
out:
unlock_page(page);
page_cache_release(page);
@@ -1030,6 +1035,7 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct address_space *mapping = inode->i_mapping;
struct shmem_inode_info *info;
struct shmem_sb_info *sbinfo;
+ struct mem_cgroup *memcg;
struct page *page;
swp_entry_t swap;
int error;
@@ -1108,8 +1114,7 @@ repeat:
goto failed;
}
- error = mem_cgroup_charge_file(page, current->mm,
- gfp & GFP_RECLAIM_MASK);
+ error = mem_cgroup_try_charge(page, current->mm, gfp, &memcg);
if (!error) {
error = shmem_add_to_page_cache(page, mapping, index,
swp_to_radix_entry(swap));
@@ -1125,12 +1130,16 @@ repeat:
* Reset swap.val? No, leave it so "failed" goes back to
* "repeat": reading a hole and writing should succeed.
*/
- if (error)
+ if (error) {
+ mem_cgroup_cancel_charge(page, memcg);
delete_from_swap_cache(page);
+ }
}
if (error)
goto failed;
+ mem_cgroup_commit_charge(page, memcg, true);
+
spin_lock(&info->lock);
info->swapped--;
shmem_recalc_inode(inode);
@@ -1168,8 +1177,7 @@ repeat:
if (sgp == SGP_WRITE)
__SetPageReferenced(page);
- error = mem_cgroup_charge_file(page, current->mm,
- gfp & GFP_RECLAIM_MASK);
+ error = mem_cgroup_try_charge(page, current->mm, gfp, &memcg);
if (error)
goto decused;
error = radix_tree_maybe_preload(gfp & GFP_RECLAIM_MASK);
@@ -1179,9 +1187,10 @@ repeat:
radix_tree_preload_end();
}
if (error) {
- mem_cgroup_uncharge_cache_page(page);
+ mem_cgroup_cancel_charge(page, memcg);
goto decused;
}
+ mem_cgroup_commit_charge(page, memcg, false);
lru_cache_add_anon(page);
spin_lock(&info->lock);