The patch titled
Subject: mm: memcontrol: do not kill uncharge batching in free_pages_and_swap_cache
has been removed from the -mm tree. Its filename was
mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache.patch
This patch was dropped because it was merged into mainline or a subsystem tree
------------------------------------------------------
From: Michal Hocko <mhocko@xxxxxxx>
Subject: 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Also update the grossly out-of-date release_pages documentation.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@xxxxxxx>
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
Reported-by: Dave Hansen <dave@xxxxxxxx>
Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/swap.c | 30 +++++++++++++++++++-----------
mm/swap_state.c | 14 ++++----------
2 files changed, 23 insertions(+), 21 deletions(-)
diff -puN mm/swap.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache mm/swap.c
--- a/mm/swap.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache
+++ a/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.
+/**
+ * release_pages - batched page_cache_release()
+ * @pages: array of pages to release
+ * @nr: number of pages
+ * @cold: whether the pages are cache cold
*
- * Avoid taking zone->lru_lock if possible, but if it is taken, retain it
- * for the remainder of the operation.
- *
- * 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,
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,
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,
if (zone)
spin_unlock_irqrestore(&zone->lru_lock,
flags);
+ lock_batch = 0;
zone = pagezone;
spin_lock_irqsave(&zone->lru_lock, flags);
}
diff -puN mm/swap_state.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache mm/swap_state.c
--- a/mm/swap_state.c~mm-memcontrol-do-not-kill-uncharge-batching-in-free_pages_and_swap_cache
+++ a/mm/swap_state.c
@@ -265,18 +265,12 @@ void free_page_and_swap_cache(struct pag
void free_pages_and_swap_cache(struct page **pages, int nr)
{
struct page **pagep = pages;
+ int i;
lru_add_drain();
- while (nr) {
- int todo = min(nr, PAGEVEC_SIZE);
- int i;
-
- for (i = 0; i < todo; i++)
- free_swap_cache(pagep[i]);
- release_pages(pagep, todo, false);
- pagep += todo;
- nr -= todo;
- }
+ for (i = 0; i < nr; i++)
+ free_swap_cache(pagep[i]);
+ release_pages(pagep, nr, false);
}
/*
_
Patches currently in -mm which might be from mhocko@xxxxxxx are
origin.patch
linux-next.patch
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