diff options
author | Michal Hocko <mhocko@suse.cz> | 2014-10-10 02:28:52 +0400 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2014-10-10 06:25:59 +0400 |
commit | aabfb57296e3dd9761e47736ec69305c95461d7d (patch) | |
tree | 379e66feb872f9f42b44b3245e52cb16ab3194bb /mm/swap.c | |
parent | 01c2965f0723a25209d5cf4cac630ed0f6d0edf4 (diff) | |
download | linux-aabfb57296e3dd9761e47736ec69305c95461d7d.tar.xz |
mm: memcontrol: do not kill uncharge batching in free_pages_and_swap_cache
free_pages_and_swap_cache limits release_pages to PAGEVEC_SIZE chunks.
This is not a big deal for the normal release path but it completely kills
memcg uncharge batching which reduces res_counter spin_lock contention.
Dave has noticed this with his page fault scalability test case on a large
machine when the lock was basically dominating on all CPUs:
80.18% 80.18% [kernel] [k] _raw_spin_lock
|
--- _raw_spin_lock
|
|--66.59%-- res_counter_uncharge_until
| res_counter_uncharge
| uncharge_batch
| uncharge_list
| mem_cgroup_uncharge_list
| release_pages
| free_pages_and_swap_cache
| tlb_flush_mmu_free
| |
| |--90.12%-- unmap_single_vma
| | unmap_vmas
| | unmap_region
| | do_munmap
| | vm_munmap
| | sys_munmap
| | system_call_fastpath
| | __GI___munmap
| |
| --9.88%-- tlb_flush_mmu
| tlb_finish_mmu
| unmap_region
| do_munmap
| vm_munmap
| sys_munmap
| system_call_fastpath
| __GI___munmap
In his case the load was running in the root memcg and that part has been
handled by reverting 05b843012335 ("mm: memcontrol: use root_mem_cgroup
res_counter") because this is a clear regression, but the problem remains
inside dedicated memcgs.
There is no reason to limit release_pages to PAGEVEC_SIZE batches other
than lru_lock held times. This logic, however, can be moved inside the
function. mem_cgroup_uncharge_list and free_hot_cold_page_list do not
hold any lock for the whole pages_to_free list so it is safe to call them
in a single run.
The release_pages() code was previously breaking the lru_lock each
PAGEVEC_SIZE pages (ie, 14 pages). However this code has no usage of
pagevecs so switch to breaking the lock at least every SWAP_CLUSTER_MAX
(32) pages. This means that the lock acquisition frequency is
approximately halved and the max hold times are approximately doubled.
The now unneeded batching is removed from free_pages_and_swap_cache().
Also update the grossly out-of-date release_pages documentation.
Signed-off-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reported-by: Dave Hansen <dave@sr71.net>
Cc: Vladimir Davydov <vdavydov@parallels.com>
Cc: Greg Thelen <gthelen@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'mm/swap.c')
-rw-r--r-- | mm/swap.c | 30 |
1 files changed, 19 insertions, 11 deletions
diff --git a/mm/swap.c b/mm/swap.c index 6b2dc3897cd5..8a12b33936b4 100644 --- a/mm/swap.c +++ b/mm/swap.c @@ -887,18 +887,14 @@ void lru_add_drain_all(void) mutex_unlock(&lock); } -/* - * Batched page_cache_release(). Decrement the reference count on all the - * passed pages. If it fell to zero then remove the page from the LRU and - * free it. - * - * Avoid taking zone->lru_lock if possible, but if it is taken, retain it - * for the remainder of the operation. +/** + * release_pages - batched page_cache_release() + * @pages: array of pages to release + * @nr: number of pages + * @cold: whether the pages are cache cold * - * The locking in this function is against shrink_inactive_list(): we recheck - * the page count inside the lock to see whether shrink_inactive_list() - * grabbed the page via the LRU. If it did, give up: shrink_inactive_list() - * will free it. + * Decrement the reference count on all the pages in @pages. If it + * fell to zero, remove the page from the LRU and free it. */ void release_pages(struct page **pages, int nr, bool cold) { @@ -907,6 +903,7 @@ void release_pages(struct page **pages, int nr, bool cold) struct zone *zone = NULL; struct lruvec *lruvec; unsigned long uninitialized_var(flags); + unsigned int uninitialized_var(lock_batch); for (i = 0; i < nr; i++) { struct page *page = pages[i]; @@ -920,6 +917,16 @@ void release_pages(struct page **pages, int nr, bool cold) continue; } + /* + * Make sure the IRQ-safe lock-holding time does not get + * excessive with a continuous string of pages from the + * same zone. The lock is held only if zone != NULL. + */ + if (zone && ++lock_batch == SWAP_CLUSTER_MAX) { + spin_unlock_irqrestore(&zone->lru_lock, flags); + zone = NULL; + } + if (!put_page_testzero(page)) continue; @@ -930,6 +937,7 @@ void release_pages(struct page **pages, int nr, bool cold) if (zone) spin_unlock_irqrestore(&zone->lru_lock, flags); + lock_batch = 0; zone = pagezone; spin_lock_irqsave(&zone->lru_lock, flags); } |