[106/227] mm: count time in drain_all_pages during direct reclaim as memory pressure

Commit Message

Andrew Morton March 22, 2022, 9:43 p.m. UTC

From: Suren Baghdasaryan <[e-mail]>
Subject: mm: count time in drain_all_pages during direct reclaim as memory pressure

When page allocation in direct reclaim path fails, the system will make
one attempt to shrink per-cpu page lists and free pages from high alloc
reserves.  Draining per-cpu pages into buddy allocator can be a very slow
operation because it's done using workqueues and the task in direct
reclaim waits for all of them to finish before proceeding.  Currently this
time is not accounted as psi memory stall.

While testing mobile devices under extreme memory pressure, when
allocations are failing during direct reclaim, we notices that psi events
which would be expected in such conditions were not triggered.  After
profiling these cases it was determined that the reason for missing psi
events was that a big chunk of time spent in direct reclaim is not
accounted as memory stall, therefore psi would not reach the levels at
which an event is generated.  Further investigation revealed that the bulk
of that unaccounted time was spent inside drain_all_pages call.

A typical captured case when drain_all_pages path gets activated:

__alloc_pages_slowpath  took 44.644.613ns
    __perform_reclaim   took    751.668ns (1.7%)
    drain_all_pages     took 43.887.167ns (98.3%)

PSI in this case records the time spent in __perform_reclaim but ignores
drain_all_pages, IOW it misses 98.3% of the time spent in
__alloc_pages_slowpath.

Annotate __alloc_pages_direct_reclaim in its entirety so that delays from
handling page allocation failure in the direct reclaim path are accounted
as memory stall.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Suren Baghdasaryan <[e-mail]>
Reported-by: Tim Murray <[e-mail]>
Acked-by: Johannes Weiner <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Reviewed-by: Shakeel Butt <[e-mail]>
Cc: Petr Mladek <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Roman Gushchin <[e-mail]>
Cc: Minchan Kim <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 mm/page_alloc.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

Patch

--- a/mm/page_alloc.c~mm-count-time-in-drain_all_pages-during-direct-reclaim-as-memory-pressure
+++ a/mm/page_alloc.c
@@ -4554,13 +4554,12 @@  __perform_reclaim(gfp_t gfp_mask, unsign
 					const struct alloc_context *ac)
 {
 	unsigned int noreclaim_flag;
-	unsigned long pflags, progress;
+	unsigned long progress;
 
 	cond_resched();
 
 	/* We now go into synchronous reclaim */
 	cpuset_memory_pressure_bump();
-	psi_memstall_enter(&pflags);
 	fs_reclaim_acquire(gfp_mask);
 	noreclaim_flag = memalloc_noreclaim_save();
 
@@ -4569,7 +4568,6 @@  __perform_reclaim(gfp_t gfp_mask, unsign
 
 	memalloc_noreclaim_restore(noreclaim_flag);
 	fs_reclaim_release(gfp_mask);
-	psi_memstall_leave(&pflags);
 
 	cond_resched();
 
@@ -4583,11 +4581,13 @@  __alloc_pages_direct_reclaim(gfp_t gfp_m
 		unsigned long *did_some_progress)
 {
 	struct page *page = NULL;
+	unsigned long pflags;
 	bool drained = false;
 
+	psi_memstall_enter(&pflags);
 	*did_some_progress = __perform_reclaim(gfp_mask, order, ac);
 	if (unlikely(!(*did_some_progress)))
-		return NULL;
+		goto out;
 
 retry:
 	page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
@@ -4603,6 +4603,8 @@  retry:
 		drained = true;
 		goto retry;
 	}
+out:
+	psi_memstall_leave(&pflags);
 
 	return page;
 }