From: Minchan Kim <minchan@kernel.org>
To: Michal Hocko <mhocko@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
hyesoo.yu@samsung.com, david@redhat.com, surenb@google.com,
pullip.cho@samsung.com, joaodias@google.com, hridya@google.com,
john.stultz@linaro.org, sumit.semwal@linaro.org,
linux-media@vger.kernel.org, devicetree@vger.kernel.org,
hch@infradead.org, robh+dt@kernel.org,
linaro-mm-sig@lists.linaro.org
Subject: Re: [PATCH v4 2/4] mm: failfast mode with __GFP_NORETRY in alloc_contig_range
Date: Thu, 28 Jan 2021 08:56:50 -0800 [thread overview]
Message-ID: <YBLs0oJY1PjCqv1q@google.com> (raw)
In-Reply-To: <YBJtdT5Tf5mRsE9U@dhcp22.suse.cz>
On Thu, Jan 28, 2021 at 08:53:25AM +0100, Michal Hocko wrote:
> On Wed 27-01-21 12:42:45, Minchan Kim wrote:
> > On Tue, Jan 26, 2021 at 08:44:49AM +0100, Michal Hocko wrote:
> > > On Mon 25-01-21 11:33:36, Minchan Kim wrote:
> > > > On Mon, Jan 25, 2021 at 02:12:00PM +0100, Michal Hocko wrote:
> > > > > On Thu 21-01-21 09:55:00, Minchan Kim wrote:
> > > > > > Contiguous memory allocation can be stalled due to waiting
> > > > > > on page writeback and/or page lock which causes unpredictable
> > > > > > delay. It's a unavoidable cost for the requestor to get *big*
> > > > > > contiguous memory but it's expensive for *small* contiguous
> > > > > > memory(e.g., order-4) because caller could retry the request
> > > > > > in different range where would have easy migratable pages
> > > > > > without stalling.
> > > > > >
> > > > > > This patch introduce __GFP_NORETRY as compaction gfp_mask in
> > > > > > alloc_contig_range so it will fail fast without blocking
> > > > > > when it encounters pages needed waiting.
> > > > >
> > > > > I am not against controling how hard this allocator tries with gfp mask
> > > > > but this changelog is rather void on any data and any user.
> > > > >
> > > > > It is also rather dubious to have retries when then caller says to not
> > > > > retry.
> > > >
> > > > Since max_tries is 1 with ++tries, it shouldn't retry.
> > >
> > > OK, I have missed that. This is a tricky code. ASYNC mode should be
> > > completely orthogonal to the retries count. Those are different things.
> > > Page allocator does an explicit bail out based on __GFP_NORETRY. You
> > > should be doing the same.
> >
> > Before sending next revision, let me check this part again.
> >
> > I want to use __GFP_NORETRY to indicate "opportunistic-easy-to-fail attempt"
> > and I want to use ASYNC migrate_mode to help the goal.
> >
> > Do you see the problem?
>
> No, as I've said. This is a normal NORETRY policy. And ASYNC migration
> is a mere implementation detail you do not have bother your users about.
> This is the semantic view. From the implementation POV it should be the
> gfp mask to drive decisions rather than a random (ASYNC) flag to control
> retries as you did here.
Make sense.
Let me cook next revision.
Thanks for the review, Michal.
next prev parent reply other threads:[~2021-01-28 16:57 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-21 17:54 [PATCH v4 0/4] Chunk Heap Support on DMA-HEAP Minchan Kim
2021-01-21 17:54 ` [PATCH v4 1/4] mm: cma: introduce gfp flag in cma_alloc instead of no_warn Minchan Kim
2021-01-21 18:46 ` David Hildenbrand
2021-01-21 18:50 ` Minchan Kim
2021-01-25 13:07 ` Michal Hocko
2021-01-25 19:42 ` Minchan Kim
2021-01-26 7:38 ` Michal Hocko
2021-01-26 19:12 ` Minchan Kim
2021-01-27 20:21 ` Minchan Kim
2021-01-21 17:55 ` [PATCH v4 2/4] mm: failfast mode with __GFP_NORETRY in alloc_contig_range Minchan Kim
2021-01-25 13:12 ` Michal Hocko
2021-01-25 13:13 ` Michal Hocko
2021-01-25 19:33 ` Minchan Kim
2021-01-26 7:44 ` Michal Hocko
2021-01-26 19:10 ` Minchan Kim
2021-01-27 8:14 ` Michal Hocko
2021-01-27 20:42 ` Minchan Kim
2021-01-28 7:53 ` Michal Hocko
2021-01-28 16:56 ` Minchan Kim [this message]
2021-01-21 17:55 ` [PATCH v4 3/4] dt-bindings: reserved-memory: Make DMA-BUF CMA heap DT-configurable Minchan Kim
2021-01-26 7:07 ` John Stultz
2021-01-27 20:25 ` Hridya Valsaraju
2021-02-05 22:55 ` Rob Herring
2021-01-21 17:55 ` [PATCH v4 4/4] dma-buf: heaps: add chunk heap to dmabuf heaps Minchan Kim
2021-01-26 7:07 ` Christoph Hellwig
2021-01-26 19:27 ` Minchan Kim
2021-01-26 7:32 ` John Stultz
2021-01-26 19:24 ` Minchan Kim
2021-01-26 7:46 ` Michal Hocko
2021-01-26 19:25 ` Minchan Kim
2021-01-27 8:09 ` Michal Hocko
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