Re: [PATCH 2/2] mm: drop PF_MEMALLOC_NORECLAIM

Dave Chinner
2024-08-28T04:11:50Z

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@suse.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@suse.com>

Looks good to me.

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

--
Dave Chinner
david@fromorbit.com