On Fri, Jul 08, 2016 at 09:21:55AM -0400, Brian Foster wrote:
> On Thu, Jun 16, 2016 at 06:21:11PM -0700, Darrick J. Wong wrote:
> > From: Dave Chinner <dchinner@xxxxxxxxxx>
> >
> > The rmap btree is allocated from the AGFL, which means we have to
> > ensure ENOSPC is reported to userspace before we run out of free
> > space in each AG. The last allocation in an AG can cause a full
> > height rmap btree split, and that means we have to reserve at least
> > this many blocks *in each AG* to be placed on the AGFL at ENOSPC.
> > Update the various space calculation functiosn to handle this.
>
> functions
>
> >
> > Also, because the macros are now executing conditional code and are called
> > quite
> > frequently, convert them to functions that initialise varaibles in the
> > struct
> > xfs_mount, use the new variables everywhere and document the calculations
> > better.
> >
> > v2: If rmapbt is disabled, it is incorrect to require 1 extra AGFL block
> > for the rmapbt (due to the + 1); the entire clause needs to be gated
> > on the feature flag.
> >
> > v3: Use m_rmap_maxlevels to determine min_free.
> >
> > [darrick.wong@xxxxxxxxxx: don't reserve blocks if !rmap]
> > [dchinner@xxxxxxxxxx: update m_ag_max_usable after growfs]
> >
> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> > Reviewed-by: Dave Chinner <dchinner@xxxxxxxxxx>
> > Signed-off-by: Dave Chinner <david@xxxxxxxxxxxxx>
> > ---
> > fs/xfs/libxfs/xfs_alloc.c | 71
> > +++++++++++++++++++++++++++++++++++++++++++++
> > fs/xfs/libxfs/xfs_alloc.h | 41 +++-----------------------
> > fs/xfs/libxfs/xfs_bmap.c | 2 +
> > fs/xfs/libxfs/xfs_sb.c | 2 +
> > fs/xfs/xfs_discard.c | 2 +
> > fs/xfs/xfs_fsops.c | 5 ++-
> > fs/xfs/xfs_log_recover.c | 1 +
> > fs/xfs/xfs_mount.c | 2 +
> > fs/xfs/xfs_mount.h | 2 +
> > fs/xfs/xfs_super.c | 2 +
> > 10 files changed, 88 insertions(+), 42 deletions(-)
> >
> >
> > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> > index 570ca17..4c8ffd4 100644
> > --- a/fs/xfs/libxfs/xfs_alloc.c
> > +++ b/fs/xfs/libxfs/xfs_alloc.c
> > @@ -63,6 +63,72 @@ xfs_prealloc_blocks(
> > }
> >
> > /*
> > + * In order to avoid ENOSPC-related deadlock caused by out-of-order
> > locking of
> > + * AGF buffer (PV 947395), we place constraints on the relationship among
> > + * actual allocations for data blocks, freelist blocks, and potential file
> > data
> > + * bmap btree blocks. However, these restrictions may result in no actual
> > space
> > + * allocated for a delayed extent, for example, a data block in a certain
> > AG is
> > + * allocated but there is no additional block for the additional bmap btree
> > + * block due to a split of the bmap btree of the file. The result of this
> > may
> > + * lead to an infinite loop when the file gets flushed to disk and all
> > delayed
> > + * extents need to be actually allocated. To get around this, we
> > explicitly set
> > + * aside a few blocks which will not be reserved in delayed allocation.
> > + *
> > + * The minimum number of needed freelist blocks is 4 fsbs _per AG_ when we
> > are
> > + * not using rmap btrees a potential split of file's bmap btree requires 1
> > fsb,
> > + * so we set the number of set-aside blocks to 4 + 4*agcount when not using
> > + * rmap btrees.
> > + *
>
> That's a bit wordy.
Yikes, that whole thing is a single sentence!
One thing I'm not really sure about is how "a potential split of file's bmap
btree requires 1 fsb" seems to translate to 4 in the actual formula. I'd
have thought it would be m_bm_maxlevels or something... not just 4.
/*
* When rmap is disabled, we need to reserve 4 fsbs _per AG_ for the freelist
* and 4 more to handle a potential split of the file's bmap btree.
*
* When rmap is enabled, we must also be able to handle two rmap btree inserts
* to record both the file data extent and a new bmbt block. The bmbt block
* might not be in the same AG as the file data extent. In the worst case
* the bmap btree splits multiple levels and all the new blocks come from
* different AGs, so set aside enough to handle rmap btree splits in all AGs.
*/
> > + * When rmap btrees are active, we have to consider that using the last
> > block
> > + * in the AG can cause a full height rmap btree split and we need enough
> > blocks
> > + * on the AGFL to be able to handle this. That means we have, in addition
> > to
> > + * the above consideration, another (2 * mp->m_rmap_levels) - 1 blocks
> > required
> > + * to be available to the free list.
>
> I'm probably missing something, but why does a full tree split require 2
> blocks per-level (minus 1)? Wouldn't that involve an allocated block per
> level (and possibly a new root block)?
The whole rmap clause is wrong. :(
I think we'll be fine with agcount * m_rmap_maxlevels.
> Otherwise, the rest looks good to me.
Cool.
<keep going downwards>
> Brian
>
> > + */
> > +unsigned int
> > +xfs_alloc_set_aside(
> > + struct xfs_mount *mp)
> > +{
> > + unsigned int blocks;
> > +
> > + blocks = 4 + (mp->m_sb.sb_agcount * XFS_ALLOC_AGFL_RESERVE);
> > + if (!xfs_sb_version_hasrmapbt(&mp->m_sb))
> > + return blocks;
> > + return blocks + (mp->m_sb.sb_agcount * (2 * mp->m_rmap_maxlevels) - 1);
> > +}
> > +
> > +/*
> > + * When deciding how much space to allocate out of an AG, we limit the
> > + * allocation maximum size to the size the AG. However, we cannot use all
> > the
> > + * blocks in the AG - some are permanently used by metadata. These
> > + * blocks are generally:
> > + * - the AG superblock, AGF, AGI and AGFL
> > + * - the AGF (bno and cnt) and AGI btree root blocks, and optionally
> > + * the AGI free inode and rmap btree root blocks.
> > + * - blocks on the AGFL according to xfs_alloc_set_aside() limits
> > + *
> > + * The AG headers are sector sized, so the amount of space they take up is
> > + * dependent on filesystem geometry. The others are all single blocks.
> > + */
> > +unsigned int
> > +xfs_alloc_ag_max_usable(struct xfs_mount *mp)
> > +{
> > + unsigned int blocks;
> > +
> > + blocks = XFS_BB_TO_FSB(mp, XFS_FSS_TO_BB(mp, 4)); /* ag headers */
> > + blocks += XFS_ALLOC_AGFL_RESERVE;
> > + blocks += 3; /* AGF, AGI btree root blocks */
> > + if (xfs_sb_version_hasfinobt(&mp->m_sb))
> > + blocks++; /* finobt root block */
> > + if (xfs_sb_version_hasrmapbt(&mp->m_sb)) {
> > + /* rmap root block + full tree split on full AG */
> > + blocks += 1 + (2 * mp->m_ag_maxlevels) - 1;
I think this could be blocks++ since we now have AG reservations.
--D
> > + }
> > +
> > + return mp->m_sb.sb_agblocks - blocks;
> > +}
> > +
> > +/*
> > * Lookup the record equal to [bno, len] in the btree given by cur.
> > */
> > STATIC int /* error */
> > @@ -1904,6 +1970,11 @@ xfs_alloc_min_freelist(
> > /* space needed by-size freespace btree */
> > min_free += min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_CNTi] + 1,
> > mp->m_ag_maxlevels);
> > + /* space needed reverse mapping used space btree */
> > + if (xfs_sb_version_hasrmapbt(&mp->m_sb))
> > + min_free += min_t(unsigned int,
> > + pag->pagf_levels[XFS_BTNUM_RMAPi] + 1,
> > + mp->m_rmap_maxlevels);
> >
> > return min_free;
> > }
> > diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
> > index 0721a48..7b6c66b 100644
> > --- a/fs/xfs/libxfs/xfs_alloc.h
> > +++ b/fs/xfs/libxfs/xfs_alloc.h
> > @@ -56,42 +56,6 @@ typedef unsigned int xfs_alloctype_t;
> > #define XFS_ALLOC_FLAG_FREEING 0x00000002 /* indicate caller is
> > freeing extents*/
> >
> > /*
> > - * In order to avoid ENOSPC-related deadlock caused by
> > - * out-of-order locking of AGF buffer (PV 947395), we place
> > - * constraints on the relationship among actual allocations for
> > - * data blocks, freelist blocks, and potential file data bmap
> > - * btree blocks. However, these restrictions may result in no
> > - * actual space allocated for a delayed extent, for example, a data
> > - * block in a certain AG is allocated but there is no additional
> > - * block for the additional bmap btree block due to a split of the
> > - * bmap btree of the file. The result of this may lead to an
> > - * infinite loop in xfssyncd when the file gets flushed to disk and
> > - * all delayed extents need to be actually allocated. To get around
> > - * this, we explicitly set aside a few blocks which will not be
> > - * reserved in delayed allocation. Considering the minimum number of
> > - * needed freelist blocks is 4 fsbs _per AG_, a potential split of file's
> > bmap
> > - * btree requires 1 fsb, so we set the number of set-aside blocks
> > - * to 4 + 4*agcount.
> > - */
> > -#define XFS_ALLOC_SET_ASIDE(mp) (4 + ((mp)->m_sb.sb_agcount * 4))
> > -
> > -/*
> > - * When deciding how much space to allocate out of an AG, we limit the
> > - * allocation maximum size to the size the AG. However, we cannot use all
> > the
> > - * blocks in the AG - some are permanently used by metadata. These
> > - * blocks are generally:
> > - * - the AG superblock, AGF, AGI and AGFL
> > - * - the AGF (bno and cnt) and AGI btree root blocks
> > - * - 4 blocks on the AGFL according to XFS_ALLOC_SET_ASIDE() limits
> > - *
> > - * The AG headers are sector sized, so the amount of space they take up is
> > - * dependent on filesystem geometry. The others are all single blocks.
> > - */
> > -#define XFS_ALLOC_AG_MAX_USABLE(mp) \
> > - ((mp)->m_sb.sb_agblocks - XFS_BB_TO_FSB(mp, XFS_FSS_TO_BB(mp, 4)) - 7)
> > -
> > -
> > -/*
> > * Argument structure for xfs_alloc routines.
> > * This is turned into a structure to avoid having 20 arguments passed
> > * down several levels of the stack.
> > @@ -133,6 +97,11 @@ typedef struct xfs_alloc_arg {
> > #define XFS_ALLOC_INITIAL_USER_DATA (1 << 1)/* special case start
> > of file */
> > #define XFS_ALLOC_USERDATA_ZERO (1 << 2)/* zero extent on
> > allocation */
> >
> > +/* freespace limit calculations */
> > +#define XFS_ALLOC_AGFL_RESERVE 4
> > +unsigned int xfs_alloc_set_aside(struct xfs_mount *mp);
> > +unsigned int xfs_alloc_ag_max_usable(struct xfs_mount *mp);
> > +
> > xfs_extlen_t xfs_alloc_longest_free_extent(struct xfs_mount *mp,
> > struct xfs_perag *pag, xfs_extlen_t need);
> > unsigned int xfs_alloc_min_freelist(struct xfs_mount *mp,
> > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> > index 2c28f2a..61c0231 100644
> > --- a/fs/xfs/libxfs/xfs_bmap.c
> > +++ b/fs/xfs/libxfs/xfs_bmap.c
> > @@ -3672,7 +3672,7 @@ xfs_bmap_btalloc(
> > args.fsbno = ap->blkno;
> >
> > /* Trim the allocation back to the maximum an AG can fit. */
> > - args.maxlen = MIN(ap->length, XFS_ALLOC_AG_MAX_USABLE(mp));
> > + args.maxlen = MIN(ap->length, mp->m_ag_max_usable);
> > args.firstblock = *ap->firstblock;
> > blen = 0;
> > if (nullfb) {
> > diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> > index f86226b..59c9f59 100644
> > --- a/fs/xfs/libxfs/xfs_sb.c
> > +++ b/fs/xfs/libxfs/xfs_sb.c
> > @@ -749,6 +749,8 @@ xfs_sb_mount_common(
> > mp->m_ialloc_min_blks = sbp->sb_spino_align;
> > else
> > mp->m_ialloc_min_blks = mp->m_ialloc_blks;
> > + mp->m_alloc_set_aside = xfs_alloc_set_aside(mp);
> > + mp->m_ag_max_usable = xfs_alloc_ag_max_usable(mp);
> > }
> >
> > /*
> > diff --git a/fs/xfs/xfs_discard.c b/fs/xfs/xfs_discard.c
> > index 272c3f8..4ff499a 100644
> > --- a/fs/xfs/xfs_discard.c
> > +++ b/fs/xfs/xfs_discard.c
> > @@ -179,7 +179,7 @@ xfs_ioc_trim(
> > * matter as trimming blocks is an advisory interface.
> > */
> > if (range.start >= XFS_FSB_TO_B(mp, mp->m_sb.sb_dblocks) ||
> > - range.minlen > XFS_FSB_TO_B(mp, XFS_ALLOC_AG_MAX_USABLE(mp)) ||
> > + range.minlen > XFS_FSB_TO_B(mp, mp->m_ag_max_usable) ||
> > range.len < mp->m_sb.sb_blocksize)
> > return -EINVAL;
> >
> > diff --git a/fs/xfs/xfs_fsops.c b/fs/xfs/xfs_fsops.c
> > index 8a85e49..3772f6c 100644
> > --- a/fs/xfs/xfs_fsops.c
> > +++ b/fs/xfs/xfs_fsops.c
> > @@ -583,6 +583,7 @@ xfs_growfs_data_private(
> > } else
> > mp->m_maxicount = 0;
> > xfs_set_low_space_thresholds(mp);
> > + mp->m_alloc_set_aside = xfs_alloc_set_aside(mp);
> >
> > /* update secondary superblocks. */
> > for (agno = 1; agno < nagcount; agno++) {
> > @@ -720,7 +721,7 @@ xfs_fs_counts(
> > cnt->allocino = percpu_counter_read_positive(&mp->m_icount);
> > cnt->freeino = percpu_counter_read_positive(&mp->m_ifree);
> > cnt->freedata = percpu_counter_read_positive(&mp->m_fdblocks) -
> > - XFS_ALLOC_SET_ASIDE(mp);
> > + mp->m_alloc_set_aside;
> >
> > spin_lock(&mp->m_sb_lock);
> > cnt->freertx = mp->m_sb.sb_frextents;
> > @@ -793,7 +794,7 @@ retry:
> > __int64_t free;
> >
> > free = percpu_counter_sum(&mp->m_fdblocks) -
> > - XFS_ALLOC_SET_ASIDE(mp);
> > + mp->m_alloc_set_aside;
> > if (!free)
> > goto out; /* ENOSPC and fdblks_delta = 0 */
> >
> > diff --git a/fs/xfs/xfs_log_recover.c b/fs/xfs/xfs_log_recover.c
> > index 0c41bd2..b33187b 100644
> > --- a/fs/xfs/xfs_log_recover.c
> > +++ b/fs/xfs/xfs_log_recover.c
> > @@ -5027,6 +5027,7 @@ xlog_do_recover(
> > xfs_warn(mp, "Failed post-recovery per-ag init: %d", error);
> > return error;
> > }
> > + mp->m_alloc_set_aside = xfs_alloc_set_aside(mp);
> >
> > xlog_recover_check_summary(log);
> >
> > diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
> > index 8af1c88..879f3ef 100644
> > --- a/fs/xfs/xfs_mount.c
> > +++ b/fs/xfs/xfs_mount.c
> > @@ -1219,7 +1219,7 @@ xfs_mod_fdblocks(
> > batch = XFS_FDBLOCKS_BATCH;
> >
> > __percpu_counter_add(&mp->m_fdblocks, delta, batch);
> > - if (__percpu_counter_compare(&mp->m_fdblocks, XFS_ALLOC_SET_ASIDE(mp),
> > + if (__percpu_counter_compare(&mp->m_fdblocks, mp->m_alloc_set_aside,
> > XFS_FDBLOCKS_BATCH) >= 0) {
> > /* we had space! */
> > return 0;
> > diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
> > index 0ed0f29..b36676c 100644
> > --- a/fs/xfs/xfs_mount.h
> > +++ b/fs/xfs/xfs_mount.h
> > @@ -123,6 +123,8 @@ typedef struct xfs_mount {
> > uint m_in_maxlevels; /* max inobt btree levels. */
> > uint m_rmap_maxlevels; /* max rmap btree levels */
> > xfs_extlen_t m_ag_prealloc_blocks; /* reserved ag blocks */
> > + uint m_alloc_set_aside; /* space we can't use */
> > + uint m_ag_max_usable; /* max space per AG */
> > struct radix_tree_root m_perag_tree; /* per-ag accounting info */
> > spinlock_t m_perag_lock; /* lock for m_perag_tree */
> > struct mutex m_growlock; /* growfs mutex */
> > diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
> > index bf63f6d..1575849 100644
> > --- a/fs/xfs/xfs_super.c
> > +++ b/fs/xfs/xfs_super.c
> > @@ -1076,7 +1076,7 @@ xfs_fs_statfs(
> > statp->f_blocks = sbp->sb_dblocks - lsize;
> > spin_unlock(&mp->m_sb_lock);
> >
> > - statp->f_bfree = fdblocks - XFS_ALLOC_SET_ASIDE(mp);
> > + statp->f_bfree = fdblocks - mp->m_alloc_set_aside;
> > statp->f_bavail = statp->f_bfree;
> >
> > fakeinos = statp->f_bfree << sbp->sb_inopblog;
> >
> > _______________________________________________
> > xfs mailing list
> > xfs@xxxxxxxxxxx
> > http://oss.sgi.com/mailman/listinfo/xfs
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