From: Michal Hocko <mhocko@kernel.org>
To: Andreas Dilger <adilger@dilger.ca>
Cc: "Theodore Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
Dave Chinner <david@fromorbit.com>,
djwong@kernel.org, Chris Mason <clm@fb.com>,
David Sterba <dsterba@suse.cz>,
ceph-devel@vger.kernel.org, cluster-devel@redhat.com,
linux-nfs@vger.kernel.org, logfs@logfs.org,
linux-xfs@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-btrfs@vger.kernel.org, linux-mtd@lists.infradead.org,
reiserfs-devel@vger.kernel.org,
linux-ntfs-dev@lists.sourceforge.net,
linux-f2fs-devel@lists.sourceforge.net,
linux-afs@lists.infradead.org,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 8/8] Revert "ext4: fix wrong gfp type under transaction"
Date: Wed, 18 Jan 2017 09:29:10 +0100 [thread overview]
Message-ID: <20170118082910.GD7015@dhcp22.suse.cz> (raw)
In-Reply-To: <7EC66AC2-1900-4328-A408-65079616A518@dilger.ca>
On Tue 17-01-17 14:04:03, Andreas Dilger wrote:
> On Jan 17, 2017, at 8:59 AM, Theodore Ts'o <tytso@mit.edu> wrote:
> >
> > On Tue, Jan 17, 2017 at 04:18:17PM +0100, Michal Hocko wrote:
> >>
> >> OK, so I've been staring into the code and AFAIU current->journal_info
> >> can contain my stored information. I could either hijack part of the
> >> word as the ref counting is only consuming low 12b. But that looks too
> >> ugly to live. Or I can allocate some placeholder.
> >
> > Yeah, I was looking at something similar. Can you guarantee that the
> > context will only take one or two bits? (Looks like it only needs one
> > bit ATM, even though at the moment you're storing the whole GFP mask,
> > correct?)
> >
> >> But before going to play with that I am really wondering whether we need
> >> all this with no journal at all. AFAIU what Jack told me it is the
> >> journal lock(s) which is the biggest problem from the reclaim recursion
> >> point of view. What would cause a deadlock in no journal mode?
> >
> > We still have the original problem for why we need GFP_NOFS even in
> > ext2. If we are in a writeback path, and we need to allocate memory,
> > we don't want to recurse back into the file system's writeback path.
> > Certainly not for the same inode, and while we could make it work if
> > the mm was writing back another inode, or another superblock, there
> > are also stack depth considerations that would make this be a bad
> > idea. So we do need to be able to assert GFP_NOFS even in no journal
> > mode, and for any file system including ext2, for that matter.
> >
> > Because of the fact that we're going to have to play games with
> > current->journal_info, maybe this is something that I should take
> > responsibility for, and to go through the the ext4 tree after the main
> > patch series go through? Maybe you could use xfs and ext2 as sample
> > (simple) implementations?
> >
> > My only ask is that the memalloc nofs context be a well defined N
> > bits, where N < 16, and I'll find some place to put them (probably
> > journal_info).
>
> I think Dave was suggesting that the NOFS context allow a pointer to
> an arbitrary struct, so that it is possible to dereference this in
> the filesystem itself to determine if the recursion is safe or not.
Yes, but can we start with a simpler approach first? Even this approach
takes quite some time to be used.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2017-01-18 8:32 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-06 14:10 [PATCH 0/8 v3] scope GFP_NOFS api Michal Hocko
2017-01-06 14:11 ` [PATCH 1/8] lockdep: allow to disable reclaim lockup detection Michal Hocko
2017-01-09 12:56 ` Vlastimil Babka
2017-01-06 14:11 ` [PATCH 2/8] xfs: abstract PF_FSTRANS to PF_MEMALLOC_NOFS Michal Hocko
2017-01-09 12:59 ` Vlastimil Babka
2017-01-09 14:29 ` Michal Hocko
2017-01-09 20:58 ` Darrick J. Wong
2017-01-06 14:11 ` [PATCH 3/8] mm: introduce memalloc_nofs_{save,restore} API Michal Hocko
2017-01-09 13:04 ` Vlastimil Babka
2017-01-09 13:42 ` Michal Hocko
2017-01-09 13:59 ` Michal Hocko
2017-01-09 14:04 ` Vlastimil Babka
2017-01-06 14:11 ` [PATCH 4/8] xfs: use memalloc_nofs_{save,restore} instead of memalloc_noio* Michal Hocko
2017-01-09 14:08 ` Vlastimil Babka
2017-01-09 14:25 ` Michal Hocko
2017-01-09 15:56 ` Brian Foster
2017-01-09 20:59 ` Darrick J. Wong
2017-01-06 14:11 ` [PATCH 5/8] jbd2: mark the transaction context with the scope GFP_NOFS context Michal Hocko
2017-01-06 14:11 ` [PATCH 6/8] jbd2: make the whole kjournald2 kthread NOFS safe Michal Hocko
2017-01-06 14:11 ` [PATCH 7/8] Revert "ext4: avoid deadlocks in the writeback path by using sb_getblk_gfp" Michal Hocko
2017-01-17 3:01 ` Theodore Ts'o
2017-01-17 7:54 ` Michal Hocko
2017-03-06 11:59 ` Michal Hocko
2017-01-06 14:11 ` [PATCH 8/8] Revert "ext4: fix wrong gfp type under transaction" Michal Hocko
2017-01-17 2:56 ` Theodore Ts'o
2017-01-17 8:24 ` Michal Hocko
2017-01-17 15:18 ` Michal Hocko
2017-01-17 15:59 ` Theodore Ts'o
2017-01-17 16:16 ` Michal Hocko
2017-01-17 17:29 ` Jan Kara
2017-01-19 8:39 ` Michal Hocko
2017-01-19 9:22 ` Jan Kara
2017-01-19 9:44 ` Michal Hocko
2017-01-26 7:44 ` Michal Hocko
2017-01-27 6:13 ` Theodore Ts'o
2017-01-27 9:37 ` Michal Hocko
2017-01-27 16:40 ` Theodore Ts'o
2017-01-28 7:32 ` [Cluster-devel] " Christoph Hellwig
2017-01-28 8:17 ` David Lang
2017-01-30 8:12 ` Michal Hocko
2017-02-03 15:32 ` Michal Hocko
2017-01-17 21:04 ` Andreas Dilger
2017-01-18 8:29 ` Michal Hocko [this message]
2017-01-06 14:18 ` [DEBUG PATCH 0/2] debug explicit GFP_NO{FS,IO} usage from the scope context Michal Hocko
2017-01-06 14:18 ` [DEBUG PATCH 1/2] mm, debug: report when GFP_NO{FS,IO} is used explicitly from memalloc_no{fs,io}_{save,restore} context Michal Hocko
2017-01-06 14:18 ` [DEBUG PATCH 2/2] silent warnings which we cannot do anything about Michal Hocko
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