linux-kernel - Re: [RFC PATCH] memalloc_noio: update the comment to make it cleaner

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Date:   Wed, 18 Sep 2019 10:14:56 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     mingo@...hat.com, peterz@...radead.org, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] memalloc_noio: update the comment to make it cleaner

On Wed 18-09-19 16:02:52, Xiubo Li wrote:
> On 2019/9/18 15:25, Michal Hocko wrote:
> > On Wed 18-09-19 04:58:20, xiubli@...hat.com wrote:
> > > From: Xiubo Li <xiubli@...hat.com>
> > > 
> > > The GFP_NOIO means all further allocations will implicitly drop
> > > both __GFP_IO and __GFP_FS flags and so they are safe for both the
> > > IO critical section and the the critical section from the allocation
> > > recursion point of view. Not only the __GFP_IO, which a bit confusing
> > > when reading the code or using the save/restore pair.
> > Historically GFP_NOIO has always implied GFP_NOFS as well. I can imagine
> > that this might come as an surprise for somebody not familiar with the
> > code though.
> 
> Yeah, it true.
> 
> >   I am wondering whether your update of the documentation
> > would be better off at __GFP_FS, __GFP_IO resp. GFP_NOFS, GFP_NOIO level.
> > This interface is simply a way to set a scoped NO{IO,FS} context.
> 
> The "Documentation/core-api/gfp_mask-from-fs-io.rst" is already very detail
> about them all.
> 
> This fixing just means to make sure that it won't surprise someone who is
> having a quickly through some code and not familiar much about the detail.
> It may make not much sense ?

Ohh, I do not think this would be senseless. I just think that the NOIO
implying NOFS as well should be described at the level where they are
documented rather than the api you have chosen.
-- 
Michal Hocko
SUSE Labs