linux-kernel - Re: [PATCH 2/2] mm: drop PF_MEMALLOC

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Message-ID: <Zs6jfv2MrubpIckX@dread.disaster.area>
Date: Wed, 28 Aug 2024 14:11:42 +1000
From: Dave Chinner <david@...morbit.com>
To: Michal Hocko <mhocko@...e.com>
Cc: Matthew Wilcox <willy@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@....de>, Yafang Shao <laoar.shao@...il.com>,
	Kent Overstreet <kent.overstreet@...ux.dev>, jack@...e.cz,
	Christian Brauner <brauner@...nel.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>, linux-fsdevel@...r.kernel.org,
	linux-mm@...ck.org, linux-bcachefs@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] mm: drop PF_MEMALLOC_NORECLAIM

On Mon, Aug 26, 2024 at 09:18:01PM +0200, Michal Hocko wrote:
> On Mon 26-08-24 18:49:23, Matthew Wilcox wrote:
> > On Mon, Aug 26, 2024 at 06:51:55PM +0200, Michal Hocko wrote:
> [...]
> > > If a plan revert is preferably, I will go with it.
> > 
> > There aren't any other users of PF_MEMALLOC_NOWARN and it definitely
> > seems like something you want at a callsite rather than blanket for every
> > allocation below this point.  We don't seem to have many PF_ flags left,
> > so let's not keep it around if there's no immediate plans for it.
> 
> Good point. What about this?
> --- 
> From 923cd429d4b1a3520c93bcf46611ae74a3158865 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Mon, 26 Aug 2024 21:15:02 +0200
> Subject: [PATCH] Revert "mm: introduce PF_MEMALLOC_NORECLAIM,
>  PF_MEMALLOC_NOWARN"
> 
> This reverts commit eab0af905bfc3e9c05da2ca163d76a1513159aa4.
> 
> There is no existing user of those flags. PF_MEMALLOC_NOWARN is
> dangerous because a nested allocation context can use GFP_NOFAIL which
> could cause unexpected failure. Such a code would be hard to maintain
> because it could be deeper in the call chain.
> 
> PF_MEMALLOC_NORECLAIM has been added even when it was pointed out [1]
> that such a allocation contex is inherently unsafe if the context
> doesn't fully control all allocations called from this context.
> 
> While PF_MEMALLOC_NOWARN is not dangerous the way PF_MEMALLOC_NORECLAIM
> is it doesn't have any user and as Matthew has pointed out we are
> running out of those flags so better reclaim it without any real users.
> 
> [1] https://lore.kernel.org/all/ZcM0xtlKbAOFjv5n@tiehlicka/
> 
> Signed-off-by: Michal Hocko <mhocko@...e.com>

Looks good to me.

Reviewed-by: Dave Chinner <dchinner@...hat.com>

-- 
Dave Chinner
david@...morbit.com