linux-kernel - Re: [PATCH mm v3] memcg: enable memory accounting in __alloc_pages

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Date:   Tue, 12 Oct 2021 17:36:10 +0200
From:   Michal Hocko <mhocko@...e.com>
To:     Vasily Averin <vvs@...tuozzo.com>
Cc:     Johannes Weiner <hannes@...xchg.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Shakeel Butt <shakeelb@...gle.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Roman Gushchin <guro@...com>,
        Uladzislau Rezki <urezki@...il.com>,
        Vlastimil Babka <vbabka@...e.cz>, cgroups@...r.kernel.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org, kernel@...nvz.org
Subject: Re: [PATCH mm v3] memcg: enable memory accounting in
 __alloc_pages_bulk

On Tue 12-10-21 17:58:21, Vasily Averin wrote:
> Enable memory accounting for bulk page allocator.

ENOCHANGELOG
 
And I have to say I am not very happy about the solution. It adds a very
tricky code where it splits different charging steps apart.

Would it be just too inefficient to charge page-by-page once all pages
are already taken away from the pcp lists? This bulk should be small so
this shouldn't really cause massive problems. I mean something like

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b37435c274cf..8bcd69195ef5 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5308,6 +5308,10 @@ unsigned long __alloc_pages_bulk(gfp_t gfp, int preferred_nid,
 
 	local_unlock_irqrestore(&pagesets.lock, flags);
 
+	if (memcg_kmem_enabled() && (gfp & __GFP_ACCOUNT)) {
+		/* charge pages here */
+	}
+
 	__count_zid_vm_events(PGALLOC, zone_idx(zone), nr_account);
 	zone_statistics(ac.preferred_zoneref->zone, zone, nr_account);
-- 
Michal Hocko
SUSE Labs