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

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Date:   Wed, 17 Feb 2021 13:32:05 -0800
From:   Minchan Kim <minchan@...nel.org>
To:     Matthew Wilcox <willy@...radead.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 09:16:12PM +0000, Matthew Wilcox wrote:
> 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.

Ah, my bad. I was confused with update side.
Okay, let's use atomic op to make it simple.

Thanks for the review, Mattew and Michal.