linux-kernel - Re: [PATCH] fs: judging context via current_is_kswapd instead of gfp

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Date:   Tue, 21 Dec 2021 15:00:20 +0000
From:   David Howells <dhowells@...hat.com>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     dhowells@...hat.com, Marc Dionne <marc.dionne@...istor.com>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        linux-cachefs@...hat.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs: judging context via current_is_kswapd instead of gfp_flag

Zhaoyang Huang <huangzhaoyang@...il.com> wrote:

> > > -             if (!(gfp_flags & __GFP_DIRECT_RECLAIM) || !(gfp_flags & __GFP_FS))
> > > +             if (current_is_kswapd() || !(gfp_flags & __GFP_FS))
> > >                       return false;
> > >               wait_on_page_fscache(page);
> ...
> If the gfp flag here is used for judging kswapd context, I think the
> answer is yes as kswapd applied __GFP_DIRECT_RECLAIM.

Now I come to look at applying it, I'm not sure whether this change is right.

I don't know if kswapd has anything to do with it.  The check is to see if
we're allowed to block at this point - and wait is just for the completion of
a DIO write to disk.

It would seem like gfpflags_allow_blocking() is the right thing to call - and
that should use current_is_kswapd() if appropriate.

David