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From: Theodore Ts'o <tytso@mit.edu>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: linux-ext4@vger.kernel.org
Subject: Re: [PATCH 16/34] libext2fs/e2fsck: refactor everyone who writes zero blocks to disk
Date: Mon, 13 Oct 2014 06:09:03 -0400	[thread overview]
Message-ID: <20141013100903.GD9738@thunk.org> (raw)
In-Reply-To: <20140913221259.13646.60917.stgit@birch.djwong.org>

On Sat, Sep 13, 2014 at 03:12:59PM -0700, Darrick J. Wong wrote:
> Convert all call sites that write zero blocks to disk to use
> ext2fs_zero_blocks2() since it can use Linux's zero out feature to do
> the writes more quickly.  Reclaim the zero buffer at freefs time and
> make the write-zeroes fallback use a larger buffer.

This patch doesn't actually convert Linux to use the zero out feature,
and I'm not entirely sure how much benefit this is going to actually
give us, since in most of the places which you are converting to use
ext2fs_zero_blocks2() is only zero'ing a block or two.

On the cost side of the equation, the first time we try to zero out a
single 4k block, this patch causes us to ignore the block allocated
and passed into ext2fs_alloc_block2(), and instead allocate a 4
megabyte buffer which is used only for ext2fs_zero_blocks2, which is
not released until e2fsck/mke2fs/resize2fs exits.

If we had reliable trim/discard that was guaranteed to zero a block
and would never be dropped by the storage device, then maybe it would
be worth it, but as it is, the only real benefit I see from this patch
is the fact that patch results in the deletion of 84 lines of code.

Maybe it would be worth it to add a ext2fs_zero_blocks3() which takes
an optional temporary buffer, much like the other if we really want to
do the code refactor?

					- Ted

P.S.  Did you really see a speedup in using a 4MB zero block buffer,
instead of a 32k block buffer?  The reason why I had chosen a stride
length of 8 was that some ten years ago, using hardware I had at my
disposal, using a larger zero buffer really didn't improve performance
any.  I'm sure that things have changed since then, but on what
systems were you testing that motivated going to a 4 meg buffer?

  reply	other threads:[~2014-10-13 10:09 UTC|newest]

Thread overview: 67+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-09-13 22:11 [PATCH 00/34] e2fsprogs Summer 2014 patchbomb, part 6 Darrick J. Wong
2014-09-13 22:11 ` [PATCH 01/34] e2fsck: offer to clear overlapping extents Darrick J. Wong
2014-09-19  1:45   ` Theodore Ts'o
2014-09-13 22:11 ` [PATCH 02/34] e2fsck: fix sliding the directory block down on bigalloc Darrick J. Wong
2014-09-19  1:45   ` Theodore Ts'o
2014-09-13 22:11 ` [PATCH 03/34] misc: zero s_jnl_blocks when adding journal online or removing external journal Darrick J. Wong
2014-09-19  1:45   ` Theodore Ts'o
2014-09-13 22:11 ` [PATCH 04/34] libext2fs: ext2fs_new_block2() should call alloc_block hook Darrick J. Wong
2014-09-13 22:11 ` [PATCH 05/34] debugfs: manage needs_recover feature when messing with the journal Darrick J. Wong
2014-09-19  6:01   ` Theodore Ts'o
2014-09-13 22:11 ` [PATCH 06/34] debugfs: add LIBINTL to debugfs link command Darrick J. Wong
2014-09-19  4:46   ` Theodore Ts'o
2014-10-17 21:07     ` Darrick J. Wong
2014-10-18 16:10       ` Theodore Ts'o
2014-09-13 22:11 ` [PATCH 07/34] ext2fs: add readahead method to improve scanning Darrick J. Wong
2014-09-19 16:15   ` Theodore Ts'o
2014-09-13 22:12 ` [PATCH 08/34] libext2fs/e2fsck: provide routines to read-ahead metadata Darrick J. Wong
2014-09-13 22:12 ` [PATCH 09/34] e2fsck: read-ahead metadata during passes 1, 2, and 4 Darrick J. Wong
2014-09-13 22:12 ` [PATCH 10/34] dumpe2fs: provide a machine-readable group-only mode Darrick J. Wong
2014-09-19 16:17   ` Theodore Ts'o
2014-09-13 22:12 ` [PATCH 11/34] dumpe2fs: output cleanup Darrick J. Wong
2014-09-19 16:22   ` Theodore Ts'o
2014-09-19 20:00     ` Darrick J. Wong
2014-10-13 18:04       ` Darrick J. Wong
2014-09-13 22:12 ` [PATCH 12/34] misc: move check_plausibility into a separate file Darrick J. Wong
2014-09-19 22:16   ` Theodore Ts'o
2014-09-13 22:12 ` [PATCH 13/34] misc: add plausibility checks to debugfs/tune2fs/dumpe2fs/e2fsck Darrick J. Wong
2014-09-19 23:00   ` Theodore Ts'o
2014-09-13 22:12 ` [PATCH 14/34] misc: use libmagic when libblkid can't identify something Darrick J. Wong
2014-09-21  5:29   ` Theodore Ts'o
2014-09-13 22:12 ` [PATCH 15/34] libext2fs: support BLKZEROOUT/FALLOC_FL_ZERO_RANGE in ext2fs_zero_blocks Darrick J. Wong
2014-09-22  2:51   ` Theodore Ts'o
2014-09-29 18:58     ` Darrick J. Wong
2014-10-14  2:58   ` Darrick J. Wong
2014-10-18 16:32   ` Theodore Ts'o
2014-10-20 23:37     ` Darrick J. Wong
2014-09-13 22:12 ` [PATCH 16/34] libext2fs/e2fsck: refactor everyone who writes zero blocks to disk Darrick J. Wong
2014-10-13 10:09   ` Theodore Ts'o [this message]
2014-10-13 17:09     ` Darrick J. Wong
2014-09-13 22:13 ` [PATCH 17/34] libext2fs: support allocating uninit blocks in bmap2() Darrick J. Wong
2014-10-13 14:35   ` Theodore Ts'o
2014-10-13 16:56     ` Darrick J. Wong
2014-10-13 18:34       ` Darrick J. Wong
2014-09-13 22:13 ` [PATCH 18/34] libext2fs: file IO routines should handle uninit blocks Darrick J. Wong
2014-09-13 22:13 ` [PATCH 19/34] resize2fs: convert fs to and from 64bit mode Darrick J. Wong
2014-09-14 17:34   ` TR Reardon
2014-09-14 17:50     ` Darrick J. Wong
2014-09-13 22:13 ` [PATCH 20/34] resize2fs: adjust reserved_gdt_blocks when changing group descriptor size Darrick J. Wong
2014-09-13 22:13 ` [PATCH 21/34] tests: test resize2fs 32->64 and 64->32bit conversion code Darrick J. Wong
2014-09-13 22:13 ` [PATCH 22/34] libext2fs: find inode goal when allocating blocks Darrick J. Wong
2014-09-13 22:13 ` [PATCH 23/34] libext2fs: find/alloc a range of empty blocks Darrick J. Wong
2014-09-13 22:13 ` [PATCH 24/34] libext2fs: add new hooks to support large allocations Darrick J. Wong
2014-09-13 22:14 ` [PATCH 25/34] libext2fs: implement fallocate Darrick J. Wong
2014-09-13 22:14 ` [PATCH 26/34] libext2fs: use fallocate for creating journals and hugefiles Darrick J. Wong
2014-09-13 22:14 ` [PATCH 27/34] debugfs: implement fallocate Darrick J. Wong
2014-09-13 22:14 ` [PATCH 28/34] tests: test debugfs punch command Darrick J. Wong
2014-09-19 16:26   ` Theodore Ts'o
2014-09-19 20:01     ` Darrick J. Wong
2014-09-13 22:14 ` [PATCH 30/34] fuse2fs: translate ACL structures Darrick J. Wong
2014-09-13 22:14 ` [PATCH 31/34] fuse2fs: handle 64-bit dates correctly Darrick J. Wong
2014-09-13 22:14 ` [PATCH 32/34] fuse2fs: implement fallocate Darrick J. Wong
2014-09-13 22:15 ` [PATCH 34/34] tests: enable using fuse2fs with metadata checksum test Darrick J. Wong
2014-09-14 17:19 ` [PATCH 35/34] e2fsck: free bh when descriptor block checksum fails Darrick J. Wong
2014-09-14 19:11   ` Eric Sandeen
2014-09-19  1:46     ` Theodore Ts'o
2014-09-18 19:09 ` [PATCH 36/34] misc: fix Coverity complaints Darrick J. Wong
2014-09-19  1:47   ` Theodore Ts'o

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