linux-kernel - Re: [PATCH v3 1/1] mm: do not increment pgfault stats when page fault handler retries

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Date:   Wed, 19 Apr 2023 19:05:04 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Suren Baghdasaryan <surenb@...gle.com>
Cc:     akpm@...ux-foundation.org, hannes@...xchg.org, mhocko@...e.com,
        josef@...icpanda.com, jack@...e.cz, ldufour@...ux.ibm.com,
        laurent.dufour@...ibm.com, michel@...pinasse.org,
        liam.howlett@...cle.com, jglisse@...gle.com, vbabka@...e.cz,
        minchan@...gle.com, dave@...olabs.net, punit.agrawal@...edance.com,
        lstoakes@...il.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kernel-team@...roid.com
Subject: Re: [PATCH v3 1/1] mm: do not increment pgfault stats when page
 fault handler retries

On Wed, Apr 19, 2023 at 10:58:36AM -0700, Suren Baghdasaryan wrote:
> If the page fault handler requests a retry, we will count the fault
> multiple times. This is a relatively harmless problem as the retry paths
> are not often requested, and the only user-visible problem is that the
> fault counter will be slightly higher than it should be.  Nevertheless,
> userspace only took one fault, and should not see the fact that the
> kernel had to retry the fault multiple times.
> Move page fault accounting into mm_account_fault() and skip incomplete
> faults which will be accounted upon completion.
> 
> Fixes: d065bd810b6d ("mm: retry page fault when blocking on disk transfer")
> Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>

Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>