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

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Message-ID: <aK6U61xNpJS0qs15@hyeyoo>
Date: Wed, 27 Aug 2025 14:17:31 +0900
From: Harry Yoo <harry.yoo@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Matthew Wilcox <willy@...radead.org>, yangshiguang1011@....com,
        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: [PATCH v3] mm: slub: avoid wake up kswapd in set_track_prepare

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?

> 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 :/

-- 
Cheers,
Harry / Hyeonggon