linux-kernel - Re:Re: [PATCH v3] mm: slub: avoid wake up kswapd in set_track

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Message-ID: <6e1ab9d8.6595.198ea7d7a78.Coremail.yangshiguang1011@163.com>
Date: Wed, 27 Aug 2025 15:45:48 +0800 (CST)
From: yangshiguang  <yangshiguang1011@....com>
To: "Harry Yoo" <harry.yoo@...cle.com>
Cc: "Vlastimil Babka" <vbabka@...e.cz>,
	"Matthew Wilcox" <willy@...radead.org>, akpm@...ux-foundation.org,
	cl@...two.org, rientjes@...gle.com, roman.gushchin@...ux.dev,
	glittao@...il.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	yangshiguang <yangshiguang@...omi.com>, stable@...r.kernel.org
Subject: Re:Re: [PATCH v3] mm: slub: avoid wake up kswapd in
 set_track_prepare





At 2025-08-27 13:17:31, "Harry Yoo" <harry.yoo@...cle.com> wrote:
>On Mon, Aug 25, 2025 at 05:42:52PM +0200, Vlastimil Babka wrote:
>> On 8/25/25 14:40, Matthew Wilcox wrote:
>> > On Mon, Aug 25, 2025 at 08:17:37PM +0800, yangshiguang1011@....com wrote:
>> >> Avoid deadlock caused by implicitly waking up kswapd by
>> >> passing in allocation flags.
>> > [...]
>> >> +	/* Preemption is disabled in ___slab_alloc() */
>> >> +	gfp_flags &= ~(__GFP_DIRECT_RECLAIM);
>> > 
>> > If you don't mean __GFP_KSWAPD_RECLAIM here, the explanation needs to
>> > be better.
>> 
>> It was suggested by Harry here:
>> https://lore.kernel.org/all/aKKhUoUkRNDkFYYb@harry
>> 
>> I think the comment is enough? Disabling preemption means we can't direct
>> reclaim, but we can wake up kswapd. If the slab caller context is such that
>> we can't, __GFP_KSWAPD_RECLAIM already won't be in the gfp_flags.
>
>To make it a little bit more verbose, this ^^ explanation can be added to the

>changelog?


ok, will be easier to understand.

>
>> But I think we should mask our also __GFP_NOFAIL and add __GFP_NOWARN?
>

>That sounds good.>
>> (we should get some common helpers for these kinds of gfp flag manipulations
>> already)
>
>Any ideas for its name?
>
>gfp_dont_try_too_hard(),
>gfp_adjust_lightweight(),
>gfp_adjust_mayfail(),
>...
>
>I'm not good at naming :/

>

How about this? 

        /* Preemption is disabled in ___slab_alloc() */
-       gfp_flags &= ~(__GFP_DIRECT_RECLAIM);
+       gfp_flags = (gfp_flags & ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL)) |
+                                       __GFP_NOWARN;

 >-- 
>Cheers,
>Harry / Hyeonggon