linux-kernel - Re: [PATCH] proc: Avoid costly high-order page allocations when reading proc files

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Message-ID: <Z-43Q__lSUta2IrM@tiehlicka>
Date: Thu, 3 Apr 2025 09:22:43 +0200
From: Michal Hocko <mhocko@...e.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>
Cc: Dave Chinner <david@...morbit.com>, Yafang Shao <laoar.shao@...il.com>,
	Harry Yoo <harry.yoo@...cle.com>, Kees Cook <kees@...nel.org>,
	joel.granados@...nel.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>,
	linux-mm@...ck.org, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] proc: Avoid costly high-order page allocations when
 reading proc files

On Wed 02-04-25 21:37:40, Shakeel Butt wrote:
> On Wed, Apr 02, 2025 at 02:24:45PM +0200, Michal Hocko wrote:
> > diff --git a/mm/util.c b/mm/util.c
> > index 60aa40f612b8..8386f6976d7d 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -601,14 +601,18 @@ static gfp_t kmalloc_gfp_adjust(gfp_t flags, size_t size)
> >  	 * We want to attempt a large physically contiguous block first because
> >  	 * it is less likely to fragment multiple larger blocks and therefore
> >  	 * contribute to a long term fragmentation less than vmalloc fallback.
> > -	 * However make sure that larger requests are not too disruptive - no
> > -	 * OOM killer and no allocation failure warnings as we have a fallback.
> > +	 * However make sure that larger requests are not too disruptive - i.e.
> > +	 * do not direct reclaim unless physically continuous memory is preferred
> > +	 * (__GFP_RETRY_MAYFAIL mode). We still kick in kswapd/kcompactd to start
> > +	 * working in the background but the allocation itself.
> >  	 */
> >  	if (size > PAGE_SIZE) {
> >  		flags |= __GFP_NOWARN;
> >  
> >  		if (!(flags & __GFP_RETRY_MAYFAIL))
> >  			flags |= __GFP_NORETRY;
> > +		else
> > +			flags &= ~__GFP_DIRECT_RECLAIM;
> 
> I think you wanted the following instead:
> 
> 		if (!(flags & __GFP_RETRY_MAYFAIL))
> 			flags &= ~__GFP_DIRECT_RECLAIM;

You are absolutely right. Not sure what I was thinking... I will send a
full patch with a changelog to wrap the situation up.

-- 
Michal Hocko
SUSE Labs