linux-kernel - Re: [patch] mm, thp: track fallbacks due to failed memcg charges separately

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Date:   Tue, 18 Feb 2020 11:26:32 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     David Rientjes <rientjes@...gle.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Jeremy Cline <jcline@...hat.com>, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [patch] mm, thp: track fallbacks due to failed memcg charges
 separately

On Mon, Feb 17, 2020 at 09:41:40PM -0800, David Rientjes wrote:
> The thp_fault_fallback stat in either /proc/vmstat is incremented if 
> either the hugepage allocation fails through the page allocator or the 
> hugepage charge fails through mem cgroup.
> 
> This patch leaves this field untouched but adds a new field,
> thp_fault_fallback_charge, which is incremented only when the mem cgroup
> charge fails.
> 
> This distinguishes between faults that want to be backed by hugepages but
> fail due to fragmentation (or low memory conditions) and those that fail
> due to mem cgroup limits.  That can be used to determine the impact of 
> fragmentation on the system by excluding faults that failed due to memcg 
> usage.
> 
> Signed-off-by: David Rientjes <rientjes@...gle.com>

The patch looks good to me, but I noticed that we miss THP_FAULT_FALLBACK
(and THP_FAULT_FALLBACK_CHARGE) accounting in shmem_getpage_gfp().

Could you fix this while you are there?
-- 
 Kirill A. Shutemov