linux-kernel - Re: [PATCH v3] mm: fix tick timer stall during deferred page init

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Message-ID: <20200326185822.6n56yl2llvdranur@ca-dmjordan1.us.oracle.com>
Date:   Thu, 26 Mar 2020 14:58:22 -0400
From:   Daniel Jordan <daniel.m.jordan@...cle.com>
To:     Shile Zhang <shile.zhang@...ux.alibaba.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] mm: fix tick timer stall during deferred page init

On Thu, Mar 19, 2020 at 03:05:12PM -0400, Daniel Jordan wrote:
> Regardless,
> Reviewed-by: Daniel Jordan <daniel.m.jordan@...cle.com>

Darn, I spoke too soon.

On a two-socket Xeon, smaller values of TICK_PAGE_COUNT caused the deferred
init timestamp to grow by over 25%.  This was with pgdatinit0 bound to the
timer interrupt CPU to make sure the issue always reproduces.

               TICK_PAGE_COUNT     node 0 deferred
                                   init time (ms)
               ---------------     ---------------
                          4096                 610
                          8192                 587
                         16384                 487
                         32768                 480    // used in the patch

Instead of trying to find a constant that lets the timer interrupt run often
enough, I think a better way forward is to reconsider how we handle the resize
lock.  I plan to prototype something and reply back with what I get.