From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Date: Thu, 3 May 2018 14:24:47 -0700 From: "Darrick J. Wong" To: Omar Sandoval Cc: xfs , linux-fsdevel , linux-mm@kvack.org, hch@infradead.org, cyberax@amazon.com, jack@suse.cz, Eryu Guan Subject: Re: [PATCH v3 1/2] iomap: add a swapfile activation function Message-ID: <20180503212447.GG4141@magnolia> References: <20180503174659.GD4127@magnolia> <20180503205803.GA26037@vader> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180503205803.GA26037@vader> Sender: owner-linux-mm@kvack.org List-ID: On Thu, May 03, 2018 at 01:58:03PM -0700, Omar Sandoval wrote: > On Thu, May 03, 2018 at 10:46:59AM -0700, Darrick J. Wong wrote: > > From: Darrick J. Wong > > > > Add a new iomap_swapfile_activate function so that filesystems can > > activate swap files without having to use the obsolete and slow bmap > > function. This enables XFS to support fallocate'd swap files and > > swap files on realtime devices. > > > > Shouldn't we also prevent the extents of an active swapfile from > becoming shared? If I swapon(a) and reflink(a, b), swapout to a now has > to break the reflink or corrupt b! In my old Btrfs swapfile series [1] I > just forbid all reflink operations on active swapfiles. xfs already does this in its reflink handler: it takes the inode lock & bails out if IS_SWAPFILE(). swapon calls claim_swapfile to take the inode lock and sets S_SWAPFILE (if successful) so the two are effectively locked out from each other... > One thing to note is that then this will need a matching > ->swap_deactivate(), which currently isn't called if ->swap_activate() > returned > 0. ...so there shouldn't be any state to undo if the iomap_swapfile_activate fails. --D > > 1: https://github.com/osandov/linux/tree/btrfs-swap > > > Signed-off-by: Darrick J. Wong > > --- > > v3: catch null iomap addr, fix too-short extent detection > > v2: document the swap file layout requirements, combine adjacent > > real/unwritten extents, align reported swap extents to physical page > > size boundaries, fix compiler errors when swap disabled