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  1. 10 9月, 2013 2 次提交
  3. 09 9月, 2013 17 次提交
  5. 06 9月, 2013 12 次提交
  7. 05 9月, 2013 2 次提交
    • J
      f2fs: optimize gc for better performance · a26b7c8a
      由 Jin Xu 提交于 
      This patch improves the gc efficiency by optimizing the victim
selection policy. With this optimization, the random re-write
performance could increase up to 20%.

For f2fs, when disk is in shortage of free spaces, gc will selects
dirty segments and moves valid blocks around for making more space
available. The gc cost of a segment is determined by the valid blocks
in the segment. The less the valid blocks, the higher the efficiency.
The ideal victim segment is the one that has the most garbage blocks.

Currently, it searches up to 20 dirty segments for a victim segment.
The selected victim is not likely the best victim for gc when there
are much more dirty segments. Why not searching more dirty segments
for a better victim? The cost of searching dirty segments is
negligible in comparison to moving blocks.

In this patch, it enlarges the MAX_VICTIM_SEARCH to 4096 to make
the search more aggressively for a possible better victim. Since
it also applies to victim selection for SSR, it will likely improve
the SSR efficiency as well.

The test case is simple. It creates as many files until the disk full.
The size for each file is 32KB. Then it writes as many as 100000
records of 4KB size to random offsets of random files in sync mode.
The testing was done on a 2GB partition of a SDHC card. Let's see the
test result of f2fs without and with the patch.

---------------------------------------
2GB partition, SDHC
create 52023 files of size 32768 bytes
random re-write 100000 records of 4KB
---------------------------------------
| file creation (s) | rewrite time (s) | gc count | gc garbage blocks |
[no patch]  341         4227             1174          174840
[patched]   324         2958             645           106682

It's obvious that, with the patch, f2fs finishes the test in 20+% less
time than without the patch. And internally it does much less gc with
higher efficiency than before.

Since the performance improvement is related to gc, it might not be so
obvious for other tests that do not trigger gc as often as this one (
This is because f2fs selects dirty segments for SSR use most of the
time when free space is in shortage). The well-known iozone test tool
was not used for benchmarking the patch becuase it seems do not have
a test case that performs random re-write on a full disk.

This patch is the revised version based on the suggestion from
Jaegeuk Kim.
Signed-off-by: NJin Xu <jinuxstyle@gmail.com>
[Jaegeuk Kim: suggested simpler solution]
Reviewed-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>
      a26b7c8a
    • J
      f2fs: merge more bios of node block writes · 423e95cc
      由 Jaegeuk Kim 提交于 
      Previously, we experience bio traces as follows when running simple sequential
write test.

 f2fs_do_submit_bio: type = NODE, io = no sync, sector = 500104928, size = 4K
 f2fs_do_submit_bio: type = NODE, io = no sync, sector = 499922208, size = 368K
 f2fs_do_submit_bio: type = NODE, io = no sync, sector = 499914752, size = 140K

 -> total 512K

The first one is to write an indirect node block, and the others are to write
direct node blocks.

The reason why there are two separate bios for direct node blocks is:
0. initial state
------------------    ------------------
|                |    |xxxxxxxx        |
------------------    ------------------

1. write 368K
------------------    ------------------
|                |    |xxxxxxxxWWWWWWWW|
------------------    ------------------

2. write 140K
------------------    ------------------
|WWWWWWW         |    |xxxxxxxxWWWWWWWW|
------------------    ------------------

This is because f2fs_write_node_pages tries to write just 512K totally, so that
we can lose the chance to merge more bios nicely.

After this patch is applied, we can get the following bio traces.

  f2fs_do_submit_bio: type = NODE, io = no sync, sector = 500103168, size = 8K
  f2fs_do_submit_bio: type = NODE, io = no sync, sector = 500111368, size = 4K
  f2fs_do_submit_bio: type = NODE, io = no sync, sector = 500107272, size = 512K
  f2fs_do_submit_bio: type = NODE, io = no sync, sector = 500108296, size = 512K
  f2fs_do_submit_bio: type = NODE, io = no sync, sector = 500109320, size = 500K

And finally, we can improve the sequential write performance,
    from 458.775 MB/s to 479.945 MB/s on SSD.
Signed-off-by: NJaegeuk Kim <jaegeuk.kim@samsung.com>
      423e95cc
  9. 04 9月, 2013 7 次提交