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

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Date:   Fri, 10 Dec 2021 09:19:50 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     David Howells <dhowells@...hat.com>
Cc:     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

On Thu, Dec 9, 2021 at 4:26 AM David Howells <dhowells@...hat.com> wrote:
>
> Huangzhaoyang <huangzhaoyang@...il.com> wrote:
>
> [adding linux-cachefs to the cc list]
>
> > Kswapd uses GFP_KERNEL as gfp_flag which make the judgment of
> > context is unexpected. fix it by using current_is_kswapd.
> >
> > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > ---
> >  fs/afs/file.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/fs/afs/file.c b/fs/afs/file.c
> > index eb11d04..6c199d5 100644
> > --- a/fs/afs/file.c
> > +++ b/fs/afs/file.c
> > @@ -485,7 +485,7 @@ static int afs_releasepage(struct page *page, gfp_t gfp_flags)
> >        * elected to wait */
> >  #ifdef CONFIG_AFS_FSCACHE
> >       if (PageFsCache(page)) {
> > -             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);
> >       }
>
> I have several of these in my fscache-rewrite branch, spread across a number
> of filesystems.  Should I fix all of them the same way?
>
> fs/9p/vfs_addr.c:               if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
> fs/afs/file.c:          if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
> fs/nfs/file.c:          if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
> fs/nfs/fscache.h:               if (!gfpflags_allow_blocking(gfp) || !(gfp & __GFP_FS))
>
> David
If the gfp flag here is used for judging kswapd context, I think the
answer is yes as kswapd applied __GFP_DIRECT_RECLAIM.
>