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Message-Id: <20140519230311.583f762c.akpm@linux-foundation.org>
Date: Mon, 19 May 2014 23:03:11 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Dave Chinner <david@...morbit.com>,
Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
riel@...hat.com, kosaki.motohiro@...fujitsu.com,
fengguang.wu@...el.com, kamezawa.hiroyu@...fujitsu.com,
linux-kernel@...r.kernel.org, xfs@....sgi.com
Subject: Re: [PATCH] mm/vmscan: Do not block forever at
shrink_inactive_list().
On Mon, 19 May 2014 22:59:15 -0700 Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue, 20 May 2014 10:44:49 +1000 Dave Chinner <david@...morbit.com> wrote:
>
> > @@ -258,14 +258,23 @@ xfs_bmapi_allocate_worker(
> > struct xfs_bmalloca *args = container_of(work,
> > struct xfs_bmalloca, work);
> > unsigned long pflags;
> > + unsigned long new_pflags = PF_FSTRANS;
> >
> > - /* we are in a transaction context here */
> > - current_set_flags_nested(&pflags, PF_FSTRANS);
> > + /*
> > + * we are in a transaction context here, but may also be doing work
> > + * in kswapd context, and hence we may need to inherit that state
> > + * temporarily to ensure that we don't block waiting for memory reclaim
> > + * in any way.
> > + */
> > + if (args->kswapd)
> > + new_pflags |= PF_MEMALLOC | PF_SWAPWRITE | PF_KSWAPD;
>
> So current_is_kswapd() returns true for a thread which is not kswapd.
> That's a bit smelly.
>
> Should this thread really be incrementing KSWAPD_INODESTEAL instead of
> PGINODESTEAL, for example? current_is_kswapd() does a range of things,
> only one(?) of which you actually want.
>
> It would be cleaner to create a new PF_ flag to select just that
> behavior. That's a better model than telling the world "I am magic and
> special".
Or a new __GFP_FLAG.
> But we're awfully close to running out of PF_ space and I don't know if
> this ugly justifies consuming a flag.
>
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