From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Jan Kara <jack@suse.cz>
Cc: kilobyte@angband.pl, darrick.wong@oracle.com, nborisov@suse.com,
linux-nvdimm@lists.01.org, david@fromorbit.com, dsterba@suse.cz,
willy@infradead.org, linux-fsdevel@vger.kernel.org, hch@lst.de,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 16/18] btrfs: Writeprotect mmap pages on snapshot
Date: Thu, 23 May 2019 16:22:39 -0500 [thread overview]
Message-ID: <20190523212239.j7jxv6amqohb2ixd@fiona> (raw)
In-Reply-To: <20190523190755.GA26522@quack2.suse.cz>
On 21:07 23/05, Jan Kara wrote:
> On Thu 23-05-19 10:27:22, Goldwyn Rodrigues wrote:
> > On 16:04 23/05, Jan Kara wrote:
> > > On Mon 29-04-19 12:26:47, Goldwyn Rodrigues wrote:
> > > > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > > >
> > > > Inorder to make sure mmap'd files don't change after snapshot,
> > > > writeprotect the mmap pages on snapshot. This is done by performing
> > > > a data writeback on the pages (which simply mark the pages are
> > > > wrprotected). This way if the user process tries to access the memory
> > > > we will get another fault and we can perform a CoW.
> > > >
> > > > In order to accomplish this, we tag all CoW pages as
> > > > PAGECACHE_TAG_TOWRITE, and add the mmapd inode in delalloc_inodes.
> > > > During snapshot, it starts writeback of all delalloc'd inodes and
> > > > here we perform a data writeback. We don't want to keep the inodes
> > > > in delalloc_inodes until it umount (WARN_ON), so we remove it
> > > > during inode evictions.
> > > >
> > > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > >
> > > OK, so here you use PAGECACHE_TAG_TOWRITE. But why is not
> > > PAGECACHE_TAG_DIRTY enough for you? Also why isn't the same needed also for
> > > normal non-DAX inodes? There you also need to trigger CoW on mmap write so
> > > I just don't see the difference...
> >
> > Because dax_writeback_mapping_range() writebacks pages marked
> > PAGECACHE_TAG_TOWRITE and not PAGECACHE_TAG_DIRTY. Should it
> > writeback pages marked as PAGECACHE_TAG_DIRTY as well?
>
> It does writeback PAGECACHE_TAG_DIRTY pages - tag_pages_for_writeback()
> moves PAGECACHE_TAG_DIRTY to PAGECACHE_TAG_TOWRITE...
Yes, I missed that. It just needs a writeback with WB_SYNC_ALL.
Thanks!
--
Goldwyn
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WARNING: multiple messages have this Message-ID (diff)
From: Goldwyn Rodrigues <rgoldwyn@suse.de>
To: Jan Kara <jack@suse.cz>
Cc: linux-btrfs@vger.kernel.org, kilobyte@angband.pl,
linux-fsdevel@vger.kernel.org, david@fromorbit.com,
willy@infradead.org, hch@lst.de, darrick.wong@oracle.com,
dsterba@suse.cz, nborisov@suse.com, linux-nvdimm@lists.01.org
Subject: Re: [PATCH 16/18] btrfs: Writeprotect mmap pages on snapshot
Date: Thu, 23 May 2019 16:22:39 -0500 [thread overview]
Message-ID: <20190523212239.j7jxv6amqohb2ixd@fiona> (raw)
In-Reply-To: <20190523190755.GA26522@quack2.suse.cz>
On 21:07 23/05, Jan Kara wrote:
> On Thu 23-05-19 10:27:22, Goldwyn Rodrigues wrote:
> > On 16:04 23/05, Jan Kara wrote:
> > > On Mon 29-04-19 12:26:47, Goldwyn Rodrigues wrote:
> > > > From: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > > >
> > > > Inorder to make sure mmap'd files don't change after snapshot,
> > > > writeprotect the mmap pages on snapshot. This is done by performing
> > > > a data writeback on the pages (which simply mark the pages are
> > > > wrprotected). This way if the user process tries to access the memory
> > > > we will get another fault and we can perform a CoW.
> > > >
> > > > In order to accomplish this, we tag all CoW pages as
> > > > PAGECACHE_TAG_TOWRITE, and add the mmapd inode in delalloc_inodes.
> > > > During snapshot, it starts writeback of all delalloc'd inodes and
> > > > here we perform a data writeback. We don't want to keep the inodes
> > > > in delalloc_inodes until it umount (WARN_ON), so we remove it
> > > > during inode evictions.
> > > >
> > > > Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> > >
> > > OK, so here you use PAGECACHE_TAG_TOWRITE. But why is not
> > > PAGECACHE_TAG_DIRTY enough for you? Also why isn't the same needed also for
> > > normal non-DAX inodes? There you also need to trigger CoW on mmap write so
> > > I just don't see the difference...
> >
> > Because dax_writeback_mapping_range() writebacks pages marked
> > PAGECACHE_TAG_TOWRITE and not PAGECACHE_TAG_DIRTY. Should it
> > writeback pages marked as PAGECACHE_TAG_DIRTY as well?
>
> It does writeback PAGECACHE_TAG_DIRTY pages - tag_pages_for_writeback()
> moves PAGECACHE_TAG_DIRTY to PAGECACHE_TAG_TOWRITE...
Yes, I missed that. It just needs a writeback with WB_SYNC_ALL.
Thanks!
--
Goldwyn
next prev parent reply other threads:[~2019-05-23 21:22 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-29 17:26 [PATCH v4 00/18] btrfs dax support Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 01/18] btrfs: create a mount option for dax Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-21 18:02 ` Darrick J. Wong
2019-05-21 18:02 ` Darrick J. Wong
2019-04-29 17:26 ` [PATCH 02/18] btrfs: Carve out btrfs_get_extent_map_write() out of btrfs_get_blocks_write() Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 04/18] dax: Introduce IOMAP_DAX_COW to CoW edges during writes Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-21 16:51 ` Darrick J. Wong
2019-05-22 20:14 ` Goldwyn Rodrigues
2019-05-22 20:14 ` Goldwyn Rodrigues
2019-05-23 2:10 ` Dave Chinner
2019-05-23 2:10 ` Dave Chinner
2019-05-23 9:05 ` Shiyang Ruan
2019-05-23 9:05 ` Shiyang Ruan
2019-05-23 11:51 ` Goldwyn Rodrigues
2019-05-23 11:51 ` Goldwyn Rodrigues
2019-05-27 8:25 ` Shiyang Ruan
2019-05-27 8:25 ` Shiyang Ruan
2019-05-28 9:17 ` Jan Kara
2019-05-28 9:17 ` Jan Kara
2019-05-29 2:01 ` Shiyang Ruan
2019-05-29 2:01 ` Shiyang Ruan
2019-05-29 2:47 ` Dave Chinner
2019-05-29 2:47 ` Dave Chinner
2019-05-29 4:02 ` Shiyang Ruan
2019-05-29 4:02 ` Shiyang Ruan
2019-05-29 4:07 ` Darrick J. Wong
2019-05-29 4:07 ` Darrick J. Wong
2019-05-29 4:46 ` Dave Chinner
2019-05-29 4:46 ` Dave Chinner
2019-05-29 13:46 ` Jan Kara
2019-05-29 13:46 ` Jan Kara
2019-05-29 22:14 ` Dave Chinner
2019-05-29 22:14 ` Dave Chinner
2019-05-30 11:16 ` Jan Kara
2019-05-30 11:16 ` Jan Kara
2019-05-30 22:59 ` Dave Chinner
2019-05-30 22:59 ` Dave Chinner
2019-04-29 17:26 ` [PATCH 05/18] btrfs: return whether extent is nocow or not Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 06/18] btrfs: Rename __endio_write_update_ordered() to btrfs_update_ordered_extent() Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
[not found] ` <20190429172649.8288-1-rgoldwyn-l3A5Bk7waGM@public.gmane.org>
2019-04-29 17:26 ` [PATCH 03/18] btrfs: basic dax read Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
[not found] ` <20190429172649.8288-4-rgoldwyn-l3A5Bk7waGM@public.gmane.org>
2019-05-21 15:14 ` Darrick J. Wong
2019-05-21 15:14 ` Darrick J. Wong
2019-05-22 21:50 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 07/18] btrfs: add dax write support Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
[not found] ` <20190429172649.8288-8-rgoldwyn-l3A5Bk7waGM@public.gmane.org>
2019-05-21 17:08 ` Darrick J. Wong
2019-05-21 17:08 ` Darrick J. Wong
2019-04-29 17:26 ` [PATCH 13/18] fs: dedup file range to use a compare function Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
[not found] ` <20190429172649.8288-14-rgoldwyn-l3A5Bk7waGM@public.gmane.org>
2019-05-21 18:17 ` Darrick J. Wong
2019-05-21 18:17 ` Darrick J. Wong
2019-04-29 17:26 ` [PATCH 18/18] btrfs: trace functions for btrfs_iomap_begin/end Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 08/18] dax: memcpy page in case of IOMAP_DAX_COW for mmap faults Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-21 17:46 ` Darrick J. Wong
2019-05-21 17:46 ` Darrick J. Wong
2019-05-22 19:11 ` Goldwyn Rodrigues
2019-05-22 19:11 ` Goldwyn Rodrigues
2019-05-23 4:02 ` Darrick J. Wong
2019-05-23 4:02 ` Darrick J. Wong
2019-05-23 12:10 ` Jan Kara
2019-05-23 12:10 ` Jan Kara
2019-04-29 17:26 ` [PATCH 09/18] btrfs: Add dax specific address_space_operations Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 10/18] dax: replace mmap entry in case of CoW Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-21 17:35 ` Darrick J. Wong
2019-05-21 17:35 ` Darrick J. Wong
2019-05-23 13:38 ` Jan Kara
2019-05-23 13:38 ` Jan Kara
2019-04-29 17:26 ` [PATCH 11/18] btrfs: add dax mmap support Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 12/18] btrfs: allow MAP_SYNC mmap Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-10 15:32 ` [PATCH for-goldwyn] btrfs: disallow MAP_SYNC outside of DAX mounts Adam Borowski
2019-05-10 15:32 ` Adam Borowski
2019-05-10 15:41 ` Dan Williams
2019-05-10 15:41 ` Dan Williams
2019-05-10 15:59 ` Pankaj Gupta
2019-05-10 15:59 ` Pankaj Gupta
2019-05-23 13:44 ` [PATCH 12/18] btrfs: allow MAP_SYNC mmap Jan Kara
2019-05-23 13:44 ` Jan Kara
2019-05-23 16:19 ` Adam Borowski
2019-05-23 16:19 ` Adam Borowski
2019-04-29 17:26 ` [PATCH 14/18] dax: memcpy before zeroing range Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-21 17:27 ` Darrick J. Wong
2019-05-21 17:27 ` Darrick J. Wong
2019-04-29 17:26 ` [PATCH 15/18] btrfs: handle dax page zeroing Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 16/18] btrfs: Writeprotect mmap pages on snapshot Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
2019-05-23 14:04 ` Jan Kara
2019-05-23 14:04 ` Jan Kara
2019-05-23 15:27 ` Goldwyn Rodrigues
2019-05-23 15:27 ` Goldwyn Rodrigues
2019-05-23 19:07 ` Jan Kara
2019-05-23 19:07 ` Jan Kara
2019-05-23 21:22 ` Goldwyn Rodrigues [this message]
2019-05-23 21:22 ` Goldwyn Rodrigues
2019-04-29 17:26 ` [PATCH 17/18] btrfs: Disable dax-based defrag and send Goldwyn Rodrigues
2019-04-29 17:26 ` Goldwyn Rodrigues
-- strict thread matches above, loose matches on Subject: below --
2019-04-16 16:41 [PATCH v3 00/18] btrfs dax support Goldwyn Rodrigues
2019-04-16 16:41 ` [PATCH 16/18] btrfs: Writeprotect mmap pages on snapshot Goldwyn Rodrigues
2019-04-16 16:41 ` Goldwyn Rodrigues
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