linux-kernel - Re: [RFC 1/2] mm: disable LRU pagevec during the migration temporarily

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Date:   Wed, 17 Feb 2021 21:16:12 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Minchan Kim <minchan@...nel.org>
Cc:     Michal Hocko <mhocko@...e.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, cgoldswo@...eaurora.org,
        linux-fsdevel@...r.kernel.org, david@...hat.com, vbabka@...e.cz,
        viro@...iv.linux.org.uk, joaodias@...gle.com
Subject: Re: [RFC 1/2] mm: disable LRU pagevec during the migration
 temporarily

On Wed, Feb 17, 2021 at 12:46:19PM -0800, Minchan Kim wrote:
> > I suspect you do not want to add atomic_read inside hot paths, right? Is
> > this really something that we have to microoptimize for? atomic_read is
> > a simple READ_ONCE on many archs.
> 
> It's also spin_lock_irq_save in some arch. If the new synchonization is
> heavily compilcated, atomic would be better for simple start but I thought
> this locking scheme is too simple so no need to add atomic operation in
> readside.

What arch uses a spinlock for atomic_read()?  I just had a quick grep and
didn't see any.