From: Minchan Kim <minchan@kernel.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Matthew Wilcox <willy@infradead.org>,
Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
cgoldswo@codeaurora.org, linux-fsdevel@vger.kernel.org,
david@redhat.com, vbabka@suse.cz, viro@zeniv.linux.org.uk,
joaodias@google.com
Subject: Re: [RFC 1/2] mm: disable LRU pagevec during the migration temporarily
Date: Thu, 18 Feb 2021 08:21:52 -0800 [thread overview]
Message-ID: <YC6UIEqNyPdRpmiq@google.com> (raw)
In-Reply-To: <YC6RGiemaQHQScsZ@dhcp22.suse.cz>
On Thu, Feb 18, 2021 at 05:08:58PM +0100, Michal Hocko wrote:
> On Thu 18-02-21 07:52:25, Minchan Kim wrote:
> > On Thu, Feb 18, 2021 at 09:17:02AM +0100, Michal Hocko wrote:
> > > On Wed 17-02-21 13:32:05, Minchan Kim wrote:
> > > > 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. This should make the code much more simple. Before you send
> > > another version for the review I have another thing to consider. You are
> > > kind of wiring this into the migration code but control over lru pcp
> > > caches can be used in other paths as well. Memory offlining would be
> > > another user. We already disable page allocator pcp caches to prevent
> > > regular draining. We could do the same with lru pcp caches.
> >
> > I didn't catch your point here. If memory offlining is interested on
> > disabling lru pcp, it could call migrate_prep and migrate_finish
> > like other places. Are you suggesting this one?
>
> What I meant to say is that you can have a look at this not as an
> integral part of the migration code but rather a common functionality
> that migration and others can use. So instead of an implicit part of
> migrate_prep this would become disable_lru_cache and migrate_finish
> would become lruc_cache_enable. See my point?
>
> An advantage of that would be that this would match the pcp page
> allocator disabling and we could have it in place for the whole
> operation to make the page state more stable wrt. LRU state (PageLRU).
Understood. Thanks for the clarification.
prev parent reply other threads:[~2021-02-18 16:21 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-16 17:03 [RFC 1/2] mm: disable LRU pagevec during the migration temporarily Minchan Kim
2021-02-16 17:03 ` [RFC 2/2] mm: fs: Invalidate BH LRU during page migration Minchan Kim
2021-02-16 18:22 ` [RFC 1/2] mm: disable LRU pagevec during the migration temporarily Matthew Wilcox
2021-02-16 21:30 ` Minchan Kim
2021-02-17 8:59 ` Michal Hocko
2021-02-17 9:50 ` Michal Hocko
2021-02-17 20:51 ` Minchan Kim
2021-02-17 21:11 ` Matthew Wilcox
2021-02-17 21:22 ` Minchan Kim
2021-02-17 20:46 ` Minchan Kim
2021-02-17 21:16 ` Matthew Wilcox
2021-02-17 21:32 ` Minchan Kim
2021-02-18 8:17 ` Michal Hocko
2021-02-18 8:24 ` David Hildenbrand
2021-02-18 15:52 ` Minchan Kim
2021-02-18 16:08 ` Michal Hocko
2021-02-18 16:21 ` Minchan Kim [this message]
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