Date:	Sat, 9 Feb 2013 20:38:57 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Zheng Liu <gnehzuil.liu@...il.com>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>,
	Jan kara <jack@...e.cz>, Dmitry Monakhov <dmonakhov@...nvz.org>
Subject: Re: [PATCH 00/10 v5] ext4: extent status tree (step2)

Hi Zheng,

Thanks for working on this!  I've included your v5 extent status tree
patches into the ext4 dev tree.  I will start doing further testing.

I suspected it wouldn't make a different, but I tested and confirmed
that your patches don't help fix the regression introduced by the
patch: disable-merging-of-uninitialized-extents

As a result, I've moved the following patches to the unstable portion
of the ext4 patch queue, pending further investigation and discussion:

disable-merging-of-uninitialized-extents
remove-unnecessary-wait-for-extent-coversion-in-ext4_fallocate
ext4_split_extent_should_take_care_of_extent_zeroout

I will be running a full set of tests and looking more deeply at the
patches, but for now I want to get them into linux-next for more
testing and review.

Cheers, 

					- Ted

On Fri, Feb 08, 2013 at 04:43:56PM +0800, Zheng Liu wrote:
> Hi all,
> 
> This is my fifth try to implement the second step of extent status tree.
> The patch set can be divided into the following parts.
> 
> Patch 1/10
>   This patch refines the extent status tree
> 
> Patch 2/10-6/10
>   These patches try to track all extent status in extent status tree and
> make it as a extent cache.  In extent_status structure bit field is removed
> because we get some warnings from 'sparse'.  Now es_pblk and es_status are
> manipulated by ext4_es_*_pblock and ext4_es_*_status directly.  Currently
> when an unwritten extent is allocated, we never know it from map->m_flags
> because ext4_ext_map_blocks doesn't return EXT4_MAP_UNWRITTEN flag.  A
> patch fixes it and we can determine the extent status according to m_flags.
>   According to Jan's feedback, we put the hole into extent cache to avoid
> to access extent tree in disk as far as possible.  Here if the whole file
> is a hole, this hole will not be cached in extent status tree because it
> is always splitted immediately.  Meanwhile the hole will not be cached
> when ext4_da_map_blocks looks up a block mapping because this hole will be
> as a delayed extent later.
> 
> Patch 7/10-8/10
>   This two patches try to reclaim memory from extent status tree when we
> are under a high memeory pressure.
> 
> Patch 9/10-10/10
>   Thses patches are picked up again from 1st version because I aware that
> they could remove a bogus wait in ext4_ind_direct_IO when dioread_nolock
> is enabled.  After applied them, the latency of dio read can be reduced.
> 
> I measure it using fio and the result shows as below.
> 
> config file
> -----------
> [global]
> ioengine=psync
> direct=1
> bs=4k
> thread
> group_reporting
> directory=/mnt/sda1/
> filename=testfile
> filesize=10g
> size=10g
> runtime=120
> iodepth=16
> 
> [fio]
> rw=randrw
> numjobs=4
> 
> result
> ------
> w/ bogus wait
>   read : io=1508.1MB, bw=12876KB/s, iops=3218 , runt=120001msec
>     clat (usec): min=128 , max=268738 , avg=718.62, stdev=3703.97
>      lat (usec): min=128 , max=268739 , avg=718.78, stdev=3703.97
>   write: io=1505.2MB, bw=12843KB/s, iops=3210 , runt=120001msec
>     clat (usec): min=47 , max=991727 , avg=520.94, stdev=3451.63
>      lat (usec): min=47 , max=991727 , avg=521.31, stdev=3451.63
> 
> w/o bogus wait
>   read : io=1576.4MB, bw=13451KB/s, iops=3362 , runt=120001msec
>     clat (usec): min=128 , max=283906 , avg=685.88, stdev=2762.64
>      lat (usec): min=128 , max=283907 , avg=686.05, stdev=2762.64
>   write: io=1577.9MB, bw=13458KB/s, iops=3364 , runt=120001msec
>     clat (usec): min=48 , max=977942 , avg=498.97, stdev=3093.08
>      lat (usec): min=48 , max=977943 , avg=499.33, stdev=3093.08
> 
> From the result we can see that the avg. of latency could be reduced a little.
> 
> changelog:
> v5 <- v4:
>  - drop a patch that removes EXT4_MAP_FROM_CLUSTER flag
>    (I will revise it in the patch set of get_block_t refinement)
>  - fold original patch 3/9 into patch 4/9
>  - manipulate es_pblk and es_status directly
>    (bit field is removed because it causes some warnings from 'sparse')
>  - let ext4_ext_map_blocks return EXT4_MAP_UNWRITTEN flag
>  - rename ext4_es_find_extent with ext4_es_find_delayed_extent
>  - add hole status and put hole into extent status tree as a cache
>  - convert unwritten extents from extent status tree in ext4_ext_direct_IO
>    and end_io callback
>  - remove a bogus wait in ext4_ind_direct_IO when dioread_nolock is enabled
> 
> v4 <- v3:
>  - register a normal shrinker to reclaim extent from extent status tree
> 
> v3 <- v2:
>  - use prune_super() to reclaim extents from extent status tree
>  - stashed es_status into es_pblk
>  - remove single extent cache
>  - rebase against 3.8-rc4
> 
> v2 <- v1:
>  - drop patches that try to improve unwritten extent conversion
>  - remove EXT4_MAP_FROM_CLUSTER flag
>  - add tracepoint for ext4_es_lookup_extent()
>  - drop a patch, which tries to fix a warning when bigalloc and delalloc
>    are enabled
>  - add a shrinker to reclaim memory from extent status tree
>  - rebase against 3.8-rc2
> 
> v4: http://lwn.net/Articles/536037/
> v3: http://lwn.net/Articles/533730/
> v2: http://lwn.net/Articles/532446/
> v1: http://lwn.net/Articles/531065/
> 
> As always, any comments or feedbacks are welcome.
> 
> FWIW, when I try to implement patch 3/10, I realize that get_block_t and
> *_map_blocks functions need to be refactored because in ext4 we already
> have six get_block_t functions
>  - ext4_get_block
>  - ext4_get_block_write
>  - ext4_get_block_write_nolock
>  - noalloc_get_block_write
>  - ext4_da_get_block_prep
>  - _ext4_get_block
> 
> and four *_map_blocks
>  - ext4_map_blocks
>  - ext4_da_map_blocks
>  - ext4_ext_map_blocks
>  - ext4_ind_map_blocks
> 
> So I am planning to refine them.  First I will try to split ext4_map_blocks
> into two parts, e.g. ext4_map_blocks_read and ext4_map_blocks_write, and 
> then try other cleanups and improvmentes.
> 
> Thanks,
> 						- Zheng
> 
> Zheng Liu (10):
>   ext4: refine extent status tree
>   ext4: add physical block and status member into extent status tree
>   ext4: let ext4_ext_map_blocks return EXT4_MAP_UNWRITTEN flag
>   ext4: track all extent status in extent status tree
>   ext4: lookup block mapping in extent status tree
>   ext4: remove single extent cache
>   ext4: adjust some functions for reclaiming extents from extent status
>     tree
>   ext4: reclaim extents from extent status tree
>   ext4: convert unwritten extents from extent status tree in end_io
>   ext4: remove bogus wait for unwritten extents in ext4_ind_direct_IO
> 
>  fs/ext4/ext4.h              |  21 +-
>  fs/ext4/ext4_extents.h      |   6 -
>  fs/ext4/extents.c           | 211 ++++--------
>  fs/ext4/extents_status.c    | 779 +++++++++++++++++++++++++++++++++++---------
>  fs/ext4/extents_status.h    |  84 ++++-
>  fs/ext4/file.c              |  16 +-
>  fs/ext4/indirect.c          |   5 -
>  fs/ext4/inode.c             | 148 +++++++--
>  fs/ext4/move_extent.c       |   3 -
>  fs/ext4/page-io.c           |   8 +-
>  fs/ext4/super.c             |   8 +-
>  include/trace/events/ext4.h | 207 ++++++++++--
>  12 files changed, 1075 insertions(+), 421 deletions(-)
> 
> -- 
> 1.7.12.rc2.18.g61b472e
> 
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