| Message ID | 20240327110318.2776850-4-hch@lst.de (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [01/13] xfs: make XFS_TRANS_LOWMODE match the other XFS_TRANS_ definitions | expand |
On Wed, Mar 27, 2024 at 12:03:08PM +0100, Christoph Hellwig wrote: > Currently xfs_bmap_del_extent_real frees RT extents before updating > the bmap btree, while it frees regular blocks after performing the bmap > btree update. While this behavior goes back to the original commit, > I can't find any good reason for handling RT extent vs regular block > freeing differently. We use the same transaction, and unless rmaps > or reflink are enabled (which currently aren't support for RT inodes) > there are no transactions rolls or deferred ops that can rely on this > ordering. ...and the realtime rmap/reflink patchsets will want to reuse the data device's ordering (bmap -> rmap -> refcount -> efi) for the rt volume. > Signed-off-by: Christoph Hellwig <hch@lst.de> I'm ok with moving this now since I'm mostly going to pave over it later anyway :) Reviewed-by: Darrick J. Wong <djwong@kernel.org> --D > --- > fs/xfs/libxfs/xfs_bmap.c | 26 +++++++++----------------- > 1 file changed, 9 insertions(+), 17 deletions(-) > > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c > index 09d4b730ee9709..282b44deb9f864 100644 > --- a/fs/xfs/libxfs/xfs_bmap.c > +++ b/fs/xfs/libxfs/xfs_bmap.c > @@ -5107,8 +5107,7 @@ xfs_bmap_del_extent_real( > { > xfs_fsblock_t del_endblock=0; /* first block past del */ > xfs_fileoff_t del_endoff; /* first offset past del */ > - int do_fx; /* free extent at end of routine */ > - int error; /* error return value */ > + int error = 0; /* error return value */ > struct xfs_bmbt_irec got; /* current extent entry */ > xfs_fileoff_t got_endoff; /* first offset past got */ > int i; /* temp state */ > @@ -5151,20 +5150,10 @@ xfs_bmap_del_extent_real( > return -ENOSPC; > > *logflagsp = XFS_ILOG_CORE; > - if (xfs_ifork_is_realtime(ip, whichfork)) { > - if (!(bflags & XFS_BMAPI_REMAP)) { > - error = xfs_rtfree_blocks(tp, del->br_startblock, > - del->br_blockcount); > - if (error) > - return error; > - } > - > - do_fx = 0; > + if (xfs_ifork_is_realtime(ip, whichfork)) > qfield = XFS_TRANS_DQ_RTBCOUNT; > - } else { > - do_fx = 1; > + else > qfield = XFS_TRANS_DQ_BCOUNT; > - } > nblks = del->br_blockcount; > > del_endblock = del->br_startblock + del->br_blockcount; > @@ -5312,18 +5301,21 @@ xfs_bmap_del_extent_real( > /* > * If we need to, add to list of extents to delete. > */ > - if (do_fx && !(bflags & XFS_BMAPI_REMAP)) { > + if (!(bflags & XFS_BMAPI_REMAP)) { > if (xfs_is_reflink_inode(ip) && whichfork == XFS_DATA_FORK) { > xfs_refcount_decrease_extent(tp, del); > + } else if (xfs_ifork_is_realtime(ip, whichfork)) { > + error = xfs_rtfree_blocks(tp, del->br_startblock, > + del->br_blockcount); > } else { > error = xfs_free_extent_later(tp, del->br_startblock, > del->br_blockcount, NULL, > XFS_AG_RESV_NONE, > ((bflags & XFS_BMAPI_NODISCARD) || > del->br_state == XFS_EXT_UNWRITTEN)); > - if (error) > - return error; > } > + if (error) > + return error; > } > > /* > -- > 2.39.2 > >
On Wed, Mar 27, 2024 at 07:55:40AM -0700, Darrick J. Wong wrote: > ...and the realtime rmap/reflink patchsets will want to reuse the data > device's ordering (bmap -> rmap -> refcount -> efi) for the rt volume. Yes. > > > Signed-off-by: Christoph Hellwig <hch@lst.de> > > I'm ok with moving this now since I'm mostly going to pave over it later > anyway :) Actually the rt extent free item and refcount work will fit in very nicely with this. Basically the rt branch added here needs another condition so that's it's skipped when using extent free items for RT. And the extent free item branch needs to pass the RT flag as already done in your series of course.
On Wed, Mar 27, 2024 at 12:03:08PM +0100, Christoph Hellwig wrote: > Currently xfs_bmap_del_extent_real frees RT extents before updating > the bmap btree, while it frees regular blocks after performing the bmap > btree update. While this behavior goes back to the original commit, > I can't find any good reason for handling RT extent vs regular block > freeing differently. It's to do with free space btree manipulations and ENOSPC. The truncate for data device extents was originally a two-phase operation. First it removed the bmapbt record, but because this can free BMBT extents, it can use up all the free space tree reservation space. So the transaction gets rolled to commit the BMBT change and the xfs_bmap_finish() call that frees the data extent runs with a new transaction reservation that allows different free space btrees to be logged without overrun. However, on crash, this could lose the free space because there was nothing to tell recovery about the extents removed from the BMBT, hence EFIs were introduced. They tie the extent free operation to the bmapbt record removal commit for recovery of the second phase of the extent removal process. Then RT extents came along. RT extent freeing does not require a free space btree reservation because the free space metadata is static and transaction size is bound. Hence we don't need to care if the BMBT record removal modifies the per-ag free space trees and we don't need a two-phase extent remove transaction. The only thing we have to care about is not losing space on crash. Hence instead of recording the extent for freeing in the bmap list for xfs_bmap_finish() to process in a new transaction, it simply freed the rtextent directly. So the original code (from 1994) simply replaced the "free AG extent later" queueing with a direct free: @@ -920,7 +937,10 @@ xfs_bmap_del_extent( (got.br_startblock == NULLSTARTBLOCK)); delay = got.br_startblock == NULLSTARTBLOCK; if (!delay) { - xfs_bmap_add_free(del->br_startblock, del->br_blockcount, flist); + if (ip->i_d.di_flags & XFS_DIFLAG_REALTIME) + xfs_rtfree_extent(ip->i_mount, ip->i_transp, del->br_startblock, del->br_blockcount); + else + xfs_bmap_add_free(del->br_startblock, del->br_blockcount, flist); del_endblock = del->br_startblock + del->br_blockcount; if (cur) xfs_bmbt_lookup_eq(cur, got.br_startoff, got.br_startblock, got.br_blockcount); This code was originally at the start of xfs_dmap_del_extent(), but the xfs_bmap_add_free() got moved to the end of the function via the "do_fx" flag (the current code logic) in 1997 because: commit c4fac74eaa580edcc6b65e977151d73f2b6e9aa5 Author: Doug Doucette <doucette@engr.sgi.com> Date: Wed Jul 9 17:34:17 1997 +0000 Fix xfs_bmap_del_extent, so it can back out of the case where an extent is being split, and the space allocation fails. There was a shutdown occurring because of a case where splitting the extent record failed because the BMBT split and the filesystem didn't have enough space for the split to be done. (FWIW, I'm not sure this can happen anymore.) The commit backed out the BMBT change on ENOSPC error, and in doing so I think this actually breaks RT free space tracking. However, it then returns an ENOSPC error, and we have a dirty transaction in the RT case so this will shut down the filesysetm when the transaction is cancelled. Hence the corrupted "bmbt now points at freed rt dev space" condition never make it to disk, but it's still the wrong way to handle the issue. IOWs, this proposed change fixes that "shutdown at ENOSPC on rt devices" situation that was introduced by the above commit back in 1997. Nice! > We use the same transaction, and unless rmaps > or reflink are enabled (which currently aren't support for RT inodes) > there are no transactions rolls or deferred ops that can rely on this > ordering. Yup, I see no problem there. Reviewed-by: Dave Chinner <dchinner@redhat.com>
FYI, I've picked up your comments with minor edits for the commit message, let me know if that is ok with you: http://git.infradead.org/?p=users/hch/xfs.git;a=commitdiff;h=445d786ae6e50f6631118e0fa378ad0cd72076a9
On Fri, Mar 29, 2024 at 05:14:26AM +0100, Christoph Hellwig wrote: > FYI, I've picked up your comments with minor edits for the commit > message, let me know if that is ok with you: > > http://git.infradead.org/?p=users/hch/xfs.git;a=commitdiff;h=445d786ae6e50f6631118e0fa378ad0cd72076a9 Yes, that's fine. It certainly can't hurt having some of the historic context of the code in new commits as it avoids the need for archive spelunking to make sense of the change... -Dave.
diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c index 09d4b730ee9709..282b44deb9f864 100644 --- a/fs/xfs/libxfs/xfs_bmap.c +++ b/fs/xfs/libxfs/xfs_bmap.c @@ -5107,8 +5107,7 @@ xfs_bmap_del_extent_real( { xfs_fsblock_t del_endblock=0; /* first block past del */ xfs_fileoff_t del_endoff; /* first offset past del */ - int do_fx; /* free extent at end of routine */ - int error; /* error return value */ + int error = 0; /* error return value */ struct xfs_bmbt_irec got; /* current extent entry */ xfs_fileoff_t got_endoff; /* first offset past got */ int i; /* temp state */ @@ -5151,20 +5150,10 @@ xfs_bmap_del_extent_real( return -ENOSPC; *logflagsp = XFS_ILOG_CORE; - if (xfs_ifork_is_realtime(ip, whichfork)) { - if (!(bflags & XFS_BMAPI_REMAP)) { - error = xfs_rtfree_blocks(tp, del->br_startblock, - del->br_blockcount); - if (error) - return error; - } - - do_fx = 0; + if (xfs_ifork_is_realtime(ip, whichfork)) qfield = XFS_TRANS_DQ_RTBCOUNT; - } else { - do_fx = 1; + else qfield = XFS_TRANS_DQ_BCOUNT; - } nblks = del->br_blockcount; del_endblock = del->br_startblock + del->br_blockcount; @@ -5312,18 +5301,21 @@ xfs_bmap_del_extent_real( /* * If we need to, add to list of extents to delete. */ - if (do_fx && !(bflags & XFS_BMAPI_REMAP)) { + if (!(bflags & XFS_BMAPI_REMAP)) { if (xfs_is_reflink_inode(ip) && whichfork == XFS_DATA_FORK) { xfs_refcount_decrease_extent(tp, del); + } else if (xfs_ifork_is_realtime(ip, whichfork)) { + error = xfs_rtfree_blocks(tp, del->br_startblock, + del->br_blockcount); } else { error = xfs_free_extent_later(tp, del->br_startblock, del->br_blockcount, NULL, XFS_AG_RESV_NONE, ((bflags & XFS_BMAPI_NODISCARD) || del->br_state == XFS_EXT_UNWRITTEN)); - if (error) - return error; } + if (error) + return error; } /*
Currently xfs_bmap_del_extent_real frees RT extents before updating the bmap btree, while it frees regular blocks after performing the bmap btree update. While this behavior goes back to the original commit, I can't find any good reason for handling RT extent vs regular block freeing differently. We use the same transaction, and unless rmaps or reflink are enabled (which currently aren't support for RT inodes) there are no transactions rolls or deferred ops that can rely on this ordering. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/xfs/libxfs/xfs_bmap.c | 26 +++++++++----------------- 1 file changed, 9 insertions(+), 17 deletions(-)