On Sat, Apr 22, 2017 at 07:53:44AM -0400, Brian Foster wrote:
> On Mon, Apr 17, 2017 at 01:52:15PM -0700, Darrick J. Wong wrote:
> > In xfs_reflink_end_cow, we erroneously reserve only enough blocks to
> > handle adding 1 extent. This is problematic if we fragment free space,
> > have to do CoW, and then have to perform multiple bmap btree expansions.
> > Furthermore, the BUI recovery routine doesn't reserve /any/ blocks to
> > handle btree splits, so log recovery fails after our first error causes
> > the filesystem to go down.
> >
> > Therefore, refactor the transaction block reservation macros until we
> > have a macro that works for our deferred (re)mapping activities, and fix
> > both problems by using that macro.
> >
> > With 1k blocks we can hit this fairly often in g/187 if the scratch fs
> > is big enough.
> >
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > ---
> > v2: avoid 64-bit division when calculating block reservation
> > ---
> > fs/xfs/libxfs/xfs_trans_space.h | 18 ++++++++++++------
> > fs/xfs/xfs_bmap_item.c | 7 ++++++-
> > fs/xfs/xfs_reflink.c | 12 ++++++++++--
> > 3 files changed, 28 insertions(+), 9 deletions(-)
> >
> > diff --git a/fs/xfs/libxfs/xfs_trans_space.h b/fs/xfs/libxfs/xfs_trans_space.h
> > index 7917f6e..04278cf 100644
> > --- a/fs/xfs/libxfs/xfs_trans_space.h
> > +++ b/fs/xfs/libxfs/xfs_trans_space.h
> > @@ -23,6 +23,16 @@
> > */
> > #define XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) \
> > (((mp)->m_rmap_mxr[0]) - ((mp)->m_rmap_mnr[0]))
> > +static inline unsigned int
> > +XFS_RMAPADD_SPACE_RES(
> > + struct xfs_mount *mp)
> > +{
> > + return xfs_sb_version_hasrmapbt(&mp->m_sb) ? mp->m_rmap_maxlevels : 0;
>
> Is the feature bit check really necessary (isn't it kind of a problem if
> we're making an rmap reservation without the feature enabled)?
You're right, we don't need this because SWAP_RMAP_SPACE_RES is only
supposed to be used for rmap-enabled swap_extents....
> > +}
> > +#define XFS_NRMAPADD_SPACE_RES(mp,b,w)\
> > + (((b + XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) - 1) / \
> > + XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp)) * \
> > + XFS_RMAPADD_SPACE_RES(mp))
> > #define XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) \
> > (((mp)->m_alloc_mxr[0]) - ((mp)->m_alloc_mnr[0]))
> > #define XFS_EXTENTADD_SPACE_RES(mp,w) (XFS_BM_MAXLEVELS(mp,w) - 1)
> > @@ -31,12 +41,8 @@
> > XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp)) * \
> > XFS_EXTENTADD_SPACE_RES(mp,w))
> > #define XFS_SWAP_RMAP_SPACE_RES(mp,b,w)\
> > - (((b + XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp) - 1) / \
> > - XFS_MAX_CONTIG_EXTENTS_PER_BLOCK(mp)) * \
> > - XFS_EXTENTADD_SPACE_RES(mp,w) + \
> > - ((b + XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) - 1) / \
> > - XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp)) * \
> > - (mp)->m_rmap_maxlevels)
> > + (XFS_NEXTENTADD_SPACE_RES((mp), (b), (w)) + \
> > + XFS_NRMAPADD_SPACE_RES((mp), (b), (w)))
> > #define XFS_DAENTER_1B(mp,w) \
> > ((w) == XFS_DATA_FORK ? (mp)->m_dir_geo->fsbcount : 1)
> > #define XFS_DAENTER_DBS(mp,w) \
> > diff --git a/fs/xfs/xfs_bmap_item.c b/fs/xfs/xfs_bmap_item.c
> > index 9bf57c7..055ab8f 100644
> > --- a/fs/xfs/xfs_bmap_item.c
> > +++ b/fs/xfs/xfs_bmap_item.c
> > @@ -34,6 +34,8 @@
> > #include "xfs_bmap.h"
> > #include "xfs_icache.h"
> > #include "xfs_trace.h"
> > +#include "xfs_bmap_btree.h"
> > +#include "xfs_trans_space.h"
> >
> >
> > kmem_zone_t *xfs_bui_zone;
> > @@ -402,6 +404,7 @@ xfs_bui_recover(
> > struct xfs_inode *ip = NULL;
> > struct xfs_defer_ops dfops;
> > xfs_fsblock_t firstfsb;
> > + unsigned int resblks;
> >
> > ASSERT(!test_bit(XFS_BUI_RECOVERED, &buip->bui_flags));
> >
> > @@ -446,7 +449,9 @@ xfs_bui_recover(
> > return -EIO;
> > }
> >
> > - error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, 0, 0, 0, &tp);
> > + resblks = XFS_SWAP_RMAP_SPACE_RES(mp, 1, XFS_DATA_FORK);
> > + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_itruncate, resblks, 0,
> > + 0, &tp);
> > if (error)
> > return error;
> > budp = xfs_trans_get_bud(tp, buip);
> > diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
> > index c0f3754..9b159f8 100644
> > --- a/fs/xfs/xfs_reflink.c
> > +++ b/fs/xfs/xfs_reflink.c
> > @@ -705,8 +705,16 @@ xfs_reflink_end_cow(
> > offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
> > end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);
> >
> > - /* Start a rolling transaction to switch the mappings */
> > - resblks = XFS_EXTENTADD_SPACE_RES(ip->i_mount, XFS_DATA_FORK);
> > + /*
> > + * Start a rolling transaction to switch the mappings. We're
> > + * unlikely ever to have to remap 16T worth of single-block
> > + * extents, so just cap the worst case extent count to 2^32-1.
> > + * Stick a warning in just in case.
> > + */
> > + WARN_ON(end_fsb - offset_fsb + 1 > ~0U);
> > + resblks = min_t(xfs_fileoff_t, ~0U, end_fsb - offset_fsb + 1);
> > + resblks = XFS_SWAP_RMAP_SPACE_RES(ip->i_mount, resblks,
...and this ought to be XFS_NEXTENTADD_SPACE_RES, because (in theory)
the per-ag reservation should cover all the rmapbt reshaping that we
could end up doing.
> > + XFS_DATA_FORK);
>
> Perhaps use U32_MAX or UINT_MAX or something rather than ~0U? Also it
> might be a good idea to point out in the comment that this is just to
> avoid 64-bit division.
Ok.
> Otherwise this seems reasonable to me, but I can't help to wonder...
> from a bigger picture standpoint, should we have already made these kind
> of block reservations before we get to I/O completion processing?
Yes -- though we've reserved bmbt split blocks when we create the da
reservation in the cow fork, we don't have a way to hold on to those
reservations from the time that we allocate the cow fork until the remap
step other than stealing them from the AGFL if we get desperate (and not
letting people reflink if it would make the AG critically low on per-ag
reservation).
Hmm. Ok, I'll respin this patch shortly to fix the near term flaws,
though fixing the reservation dropping is a longer term fix...
--D
>
> Brian
>
> > error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
> > resblks, 0, 0, &tp);
> > if (error)
> > --
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