Re: [PATCH 6/6] xfs: reduce transaction reservation for freeing extents

Darrick J. Wong
2021-05-27T06:19:49Z

On Thu, May 27, 2021 at 02:52:02PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> Ever since we moved to deferred freeing of extents, we only every
> free one extent per transaction. We separated the bulk unmapping of
> extents from the submission of EFI/free/EFD transactions, and hence
> while we unmap extents in bulk, we only every free one per
> transaction.
>
> Our transaction reservations still live in the era from before
> deferred freeing of extents, so still refer to "xfs_bmap_finish"
> and it needing to free multiple extents per transaction. These
> freeing reservations can now all be reduced to a single extent to
> reflect how we currently free extents.
>
> This significantly reduces the reservation sizes for operations like
> truncate and directory operations where they currently reserve space
> for freeing up to 4 extents per transaction.
>
> For a 4kB block size filesytsem with reflink=1,rmapbt=1, the
> reservation sizes change like this:
>
> Reservation Before After
> (index) logres logcount logres logcount
> 0 write 314104 8 314104 8
> 1 itruncate 579456 8 148608 8
> 2 rename 435840 2 307936 2
> 3 link 191600 2 191600 2
> 4 remove 312960 2 174328 2
> 5 symlink 470656 3 470656 3
> 6 create 469504 2 469504 2
> 7 create_tmpfile 490240 2 490240 2
> 8 mkdir 469504 3 469504 3
> 9 ifree 508664 2 508664 2
> 10 ichange 5752 0 5752 0
> 11 growdata 147840 2 147840 2
> 12 addafork 178936 2 178936 2
> 13 writeid 760 0 760 0
> 14 attrinval 578688 1 147840 1
> 15 attrsetm 26872 3 26872 3
> 16 attrsetrt 16896 0 16896 0
> 17 attrrm 292224 3 148608 3
> 18 clearagi 4224 0 4224 0
> 19 growrtalloc 173944 2 173944 2
> 20 growrtzero 4224 0 4224 0
> 21 growrtfree 10096 0 10096 0
> 22 qm_setqlim 232 1 232 1
> 23 qm_dqalloc 318327 8 318327 8
> 24 qm_quotaoff 4544 1 4544 1
> 25 qm_equotaoff 320 1 320 1
> 26 sb 4224 1 4224 1
> 27 fsyncts 760 0 760 0
> MAX 579456 8 318327 8
>
> So we can see that many of the reservations have gone substantially
> down in size. itruncate, rename, remove, attrinval and attrrm are
> much smaller now. The maximum reservation size has gone from being
> attrinval at 579456*8 bytes to dqalloc at 318327*8 bytes. This is a
> substantial improvement for common operations.

If you're going to play around with log reservations, can you have a
quick look at the branch I made to fix all the oversized reservations
that we make for rmap and reflink?

https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git/log/?h=reflink-speedups

That's what's next after deferred inode inactivation lands.

--D

>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/libxfs/xfs_trans_resv.c | 63 +++++++++++++++++-----------------
> 1 file changed, 31 insertions(+), 32 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
> index 02079f55ef20..f5e76eeae281 100644
> --- a/fs/xfs/libxfs/xfs_trans_resv.c
> +++ b/fs/xfs/libxfs/xfs_trans_resv.c
> @@ -232,8 +232,7 @@ xfs_rtalloc_log_count(
> * Various log reservation values.
> *
> * These are based on the size of the file system block because that is what
> - * most transactions manipulate. Each adds in an additional 128 bytes per
> - * item logged to try to account for the overhead of the transaction mechanism.
> + * most transactions manipulate.
> *
> * Note: Most of the reservations underestimate the number of allocation
> * groups into which they could free extents in the xfs_defer_finish() call.
> @@ -262,9 +261,9 @@ xfs_rtalloc_log_count(
> * the superblock free block counter: sector size
> * the realtime bitmap: ((MAXEXTLEN / rtextsize) / NBBY) bytes
> * the realtime summary: 1 block
> - * And the bmap_finish transaction can free bmap blocks in a join (t3):
> + * And the deferred freeing can free bmap blocks in a join (t3):
> * the super block free block counter: sector size
> - * two extent allocfree reservations for the AG.
> + * one extent allocfree reservation for the AG.
> */
> STATIC uint
> xfs_calc_write_reservation(
> @@ -290,23 +289,25 @@ xfs_calc_write_reservation(
> }
>
> t3 = xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_allocfree_extent_res(mp) * 2;
> + xfs_allocfree_extent_res(mp);
>
> return XFS_DQUOT_LOGRES(mp) + max3(t1, t2, t3);
> }
>
> /*
> - * In truncating a file we free up to two extents at once. We can modify (t1):
> + * In truncating a file we defer freeing so we only free one extent per
> + * transaction for normal files. For rt files we limit to 2 extents per
> + * transaction.
> + * We can modify (t1):
> * the inode being truncated: inode size
> * the inode's bmap btree: (max depth + 1) * block size
> - * And the bmap_finish transaction can free the blocks and bmap blocks (t2):
> - * the super block to reflect the freed blocks: sector size
> - * four extent allocfree reservations for the AG.
> - * Or, if it's a realtime file (t3):
> + * Or, if it's a realtime file (t2):
> * the super block to reflect the freed blocks: sector size
> * the realtime bitmap: 2 exts * ((MAXEXTLEN / rtextsize) / NBBY) bytes
> * the realtime summary: 2 exts * 1 block
> - * two extent allocfree reservations for the AG.
> + * And the deferred freeing can free the blocks and bmap blocks (t3):
> + * the super block to reflect the freed blocks: sector size
> + * one extent allocfree reservation for the AG.
> */
> STATIC uint
> xfs_calc_itruncate_reservation(
> @@ -318,17 +319,16 @@ xfs_calc_itruncate_reservation(
> t1 = xfs_calc_inode_res(mp, 1) +
> xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK) + 1, blksz);
>
> - t2 = xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_allocfree_extent_res(mp) * 4;
> -
> if (xfs_sb_version_hasrealtime(&mp->m_sb)) {
> - t3 = xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_calc_buf_res(xfs_rtalloc_log_count(mp, 2), blksz) +
> - xfs_allocfree_extent_res(mp) * 2;
> + t2 = xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> + xfs_calc_buf_res(xfs_rtalloc_log_count(mp, 2), blksz);
> } else {
> - t3 = 0;
> + t2 = 0;
> }
>
> + t3 = xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> + xfs_allocfree_extent_res(mp);
> +
> return XFS_DQUOT_LOGRES(mp) + max3(t1, t2, t3);
> }
>
> @@ -337,10 +337,9 @@ xfs_calc_itruncate_reservation(
> * the four inodes involved: 4 * inode size
> * the two directory btrees: 2 * (max depth + v2) * dir block size
> * the two directory bmap btrees: 2 * max depth * block size
> - * And the bmap_finish transaction can free dir and bmap blocks (two sets
> - * of bmap blocks) giving:
> + * And the deferred freeing can free dir and bmap blocks giving:
> * the superblock for the free block count: sector size
> - * three extent allocfree reservations for the AG.
> + * one extent allocfree reservations for the AG.
> */
> STATIC uint
> xfs_calc_rename_reservation(
> @@ -351,7 +350,7 @@ xfs_calc_rename_reservation(
> xfs_calc_buf_res(2 * XFS_DIROP_LOG_COUNT(mp),
> XFS_FSB_TO_B(mp, 1))),
> (xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_allocfree_extent_res(mp) * 3));
> + xfs_allocfree_extent_res(mp)));
> }
>
> /*
> @@ -375,7 +374,7 @@ xfs_calc_iunlink_remove_reservation(
> * the linked inode: inode size
> * the directory btree could split: (max depth + v2) * dir block size
> * the directory bmap btree could join or split: (max depth + v2) * blocksize
> - * And the bmap_finish transaction can free some bmap blocks giving:
> + * And the deferred freeing can free bmap blocks giving:
> * the superblock for the free block count: sector size
> * one extent allocfree reservation for the AG.
> */
> @@ -411,9 +410,9 @@ xfs_calc_iunlink_add_reservation(xfs_mount_t *mp)
> * the removed inode: inode size
> * the directory btree could join: (max depth + v2) * dir block size
> * the directory bmap btree could join or split: (max depth + v2) * blocksize
> - * And the bmap_finish transaction can free the dir and bmap blocks giving:
> + * And the deferred freeing can free the dir and bmap blocks giving:
> * the superblock for the free block count: sector size
> - * two extent allocfree reservations for the AG.
> + * one extent allocfree reservation for the AG.
> */
> STATIC uint
> xfs_calc_remove_reservation(
> @@ -425,7 +424,7 @@ xfs_calc_remove_reservation(
> xfs_calc_buf_res(XFS_DIROP_LOG_COUNT(mp),
> XFS_FSB_TO_B(mp, 1))),
> (xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_allocfree_extent_res(mp) * 2));
> + xfs_allocfree_extent_res(mp)));
> }
>
> /*
> @@ -670,9 +669,9 @@ xfs_calc_addafork_reservation(
> * Removing the attribute fork of a file
> * the inode being truncated: inode size
> * the inode's bmap btree: max depth * block size
> - * And the bmap_finish transaction can free the blocks and bmap blocks:
> + * And the deferred freeing can free the blocks and bmap blocks:
> * the super block to reflect the freed blocks: sector size
> - * four extent allocfree reservations for the AG.
> + * one extent allocfree reservation for the AG.
> */
> STATIC uint
> xfs_calc_attrinval_reservation(
> @@ -682,7 +681,7 @@ xfs_calc_attrinval_reservation(
> xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_ATTR_FORK),
> XFS_FSB_TO_B(mp, 1))),
> (xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_allocfree_extent_res(mp) * 4));
> + xfs_allocfree_extent_res(mp)));
> }
>
> /*
> @@ -730,9 +729,9 @@ xfs_calc_attrsetrt_reservation(
> * the inode: inode size
> * the attribute btree could join: max depth * block size
> * the inode bmap btree could join or split: max depth * block size
> - * And the bmap_finish transaction can free the attr blocks freed giving:
> + * And the deferred freeing can free the attr blocks freed giving:
> * the superblock for the free block count: sector size
> - * two extent allocfree reservations for the AG.
> + * one extent allocfree reservations for the AG.
> */
> STATIC uint
> xfs_calc_attrrm_reservation(
> @@ -746,7 +745,7 @@ xfs_calc_attrrm_reservation(
> XFS_BM_MAXLEVELS(mp, XFS_ATTR_FORK)) +
> xfs_calc_buf_res(XFS_BM_MAXLEVELS(mp, XFS_DATA_FORK), 0)),
> (xfs_calc_buf_res(1, mp->m_sb.sb_sectsize) +
> - xfs_allocfree_extent_res(mp) * 2));
> + xfs_allocfree_extent_res(mp)));
> }
>
> /*
> --
> 2.31.1
>