From: Michal Hocko <mhocko@kernel.org>
To: Wei Yang <richard.weiyang@gmail.com>
Cc: linux-mm@kvack.org, Vlastimil Babka <vbabka@suse.cz>,
Johannes Weiner <hannes@cmpxchg.org>,
Mel Gorman <mgorman@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 2/4] mm, tree wide: replace __GFP_REPEAT by __GFP_RETRY_MAYFAIL with more useful semantic
Date: Fri, 9 Jun 2017 09:32:44 +0200 [thread overview]
Message-ID: <20170609073244.GA21764@dhcp22.suse.cz> (raw)
In-Reply-To: <20170607015909.GA6596@WeideMBP.lan>
On Wed 07-06-17 10:10:36, Wei Yang wrote:
[...]
> Hmm... Let me be more specific. With two factors, costly or not, flag set or
> not, we have four combinations. Here it is classified into two categories.
>
> 1. __GFP_RETRY_MAYFAIL not set
>
> Brief description on behavior:
> costly: pick up the shortcut, so no OOM
> !costly: no shortcut and will OOM I think
>
> Impact from this patch set:
> No.
true
> My personal understanding:
> The allocation without __GFP_RETRY_MAYFAIL is not effected by this patch
> set. Since !costly allocation will trigger OOM, this is the reason why
> "small allocations never fail _practically_", as mentioned in
> https://lwn.net/Articles/723317/.
>
>
> 3. __GFP_RETRY_MAYFAIL set
>
> Brief description on behavior:
> costly/!costly: no shortcut here and no OOM invoked
>
> Impact from this patch set:
> For those allocations with __GFP_RETRY_MAYFAIL, OOM is not invoked for
> both.
yes
> My personal understanding:
> This is the semantic you are willing to introduce in this patch set. By
> cutting off the OOM invoke when __GFP_RETRY_MAYFAIL is set, you makes this
> a middle situation between NOFAIL and NORETRY.
yes
> page_alloc will try some luck to get some free pages without disturb other
> part of the system. By doing so, the never fail allocation for !costly
> pages will be "fixed". If I understand correctly, you are willing to make
> this the default behavior in the future?
I do not think we can make this a default in a foreseeable future
unfortunately. That's why I've made it a gfp modifier in the first
place. I assume many users will opt in by using the flag. In future we
can even help by adding a highlevel GFP_$FOO flag but I am worried that
this would just add to the explosion of existing highlevel gfp masks
(e.g. do we want GFP_NOFS_MAY_FAIL, GFP_USER_MAY_FAIL,
GFP_USER_HIGH_MOVABLE_MAYFAIL etc...)
--
Michal Hocko
SUSE Labs
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next prev parent reply other threads:[~2017-06-09 7:32 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-07 15:48 [RFC PATCH 0/4 v2] mm: give __GFP_REPEAT a better semantic Michal Hocko
2017-03-07 15:48 ` [PATCH 1/4] s390: get rid of superfluous __GFP_REPEAT Michal Hocko
2017-03-08 8:23 ` Heiko Carstens
2017-03-08 14:11 ` Michal Hocko
2017-03-09 8:27 ` Heiko Carstens
2017-03-07 15:48 ` [RFC PATCH 2/4] mm, tree wide: replace __GFP_REPEAT by __GFP_RETRY_MAYFAIL with more useful semantic Michal Hocko
2017-05-25 1:21 ` NeilBrown
2017-05-31 11:42 ` Michal Hocko
2017-06-03 2:24 ` Wei Yang
2017-06-05 6:43 ` Michal Hocko
2017-06-06 3:04 ` Wei Yang
2017-06-06 12:03 ` Michal Hocko
2017-06-07 2:10 ` Wei Yang
2017-06-09 7:32 ` Michal Hocko [this message]
2017-03-07 15:48 ` [RFC PATCH 3/4] xfs: map KM_MAYFAIL to __GFP_RETRY_MAYFAIL Michal Hocko
2017-03-07 17:05 ` Darrick J. Wong
2017-03-08 9:35 ` Michal Hocko
2017-03-08 11:23 ` Tetsuo Handa
2017-03-08 12:54 ` Michal Hocko
2017-03-08 15:06 ` Christoph Hellwig
2017-03-09 9:16 ` Michal Hocko
2017-03-07 15:48 ` [RFC PATCH 4/4] mm: kvmalloc support __GFP_RETRY_MAYFAIL for all sizes Michal Hocko
2017-05-16 9:10 ` [RFC PATCH 0/4 v2] mm: give __GFP_REPEAT a better semantic Michal Hocko
2017-05-23 8:12 ` Vlastimil Babka
2017-05-24 1:06 ` NeilBrown
2017-05-24 7:34 ` Michal Hocko
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