linux-kernel - Re: [PATCH STABLE 4.4-5.3] mm, vmstat: drop zone->lock in /proc/pagetypeinfo

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Date:   Thu, 27 May 2021 11:15:25 +0200
From:   Greg KH <greg@...ah.com>
To:     Stephen Brennan <stephen.s.brennan@...cle.com>
Cc:     stable@...r.kernel.org, Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <clameter@....com>,
        Mel Gorman <mel@....ul.ie>, Andy Whitcroft <apw@...dowen.org>,
        Aruna Ramakrishna <aruna.ramakrishna@...cle.com>,
        Khalid Aziz <khalid.aziz@...cle.com>
Subject: Re: [PATCH STABLE 4.4-5.3] mm, vmstat: drop zone->lock in
 /proc/pagetypeinfo

On Wed, May 26, 2021 at 10:46:13AM -0700, Stephen Brennan wrote:
> Commit 93b3a674485f6a4b8ffff85d1682d5e8b7c51560 upstream
> 
> Commit 93b3a674485f ("mm,vmstat: reduce zone->lock holding time by
> /proc/pagetypeinfo") upstream caps the number of iterations over each
> free_list at 100,000, and also drops the zone->lock in between each
> migrate type. Capping the iteration count alters the file contents in
> some cases, which means this approach may not be suitable for stable
> backports.
> 
> However, dropping zone->lock in between migrate types (and, as a result,
> page orders) will not change the /proc/pagetypeinfo file contents. It
> can significantly reduce the length of time spent with IRQs disabled,
> which can prevent missed interrupts or soft lockups which we have
> observed on systems with particularly large memory.
> 
> Thus, this commit is a modified version of the upstream one which only
> drops the lock in between migrate types.

Now queued up, thanks.

greg k-h