Linux-Devicetree Archive on lore.kernel.org
 help / color / Atom feed
From: Michal Hocko <mhocko@suse.com>
To: Minchan Kim <minchan@kernel.org>
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 08:53:25 +0100
Message-ID: <YBJtdT5Tf5mRsE9U@dhcp22.suse.cz> (raw)
In-Reply-To: <YBHQRY8kw8/wjFK8@google.com>

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.

-- 
Michal Hocko
SUSE Labs

  reply index

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 [this message]
2021-01-28 16:56             ` Minchan Kim
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=YBJtdT5Tf5mRsE9U@dhcp22.suse.cz \
    --to=mhocko@suse.com \
    --cc=akpm@linux-foundation.org \
    --cc=david@redhat.com \
    --cc=devicetree@vger.kernel.org \
    --cc=hch@infradead.org \
    --cc=hridya@google.com \
    --cc=hyesoo.yu@samsung.com \
    --cc=joaodias@google.com \
    --cc=john.stultz@linaro.org \
    --cc=linaro-mm-sig@lists.linaro.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-media@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=minchan@kernel.org \
    --cc=pullip.cho@samsung.com \
    --cc=robh+dt@kernel.org \
    --cc=sumit.semwal@linaro.org \
    --cc=surenb@google.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Devicetree Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-devicetree/0 linux-devicetree/git/0.git
	git clone --mirror https://lore.kernel.org/linux-devicetree/1 linux-devicetree/git/1.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-devicetree linux-devicetree/ https://lore.kernel.org/linux-devicetree \
		devicetree@vger.kernel.org
	public-inbox-index linux-devicetree

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-devicetree


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git