On 2017/5/24 12:14, Jaegeuk Kim wrote:
Hi Pengyang,
Could you please shed a light on some performance gains by this?
Hi, Jaegeuk,
Sorry for replying so late.
I've tested the duration of nat-radix-tree traveling and list-sort of
nat-entry, it is about *100us* averagely during fragmentation(arm64 mobile).
100us seems nobody for CP, but I still think it make senses for scenario
where massive dirty nat_entries exist in system(corner case, hard to
produce).
Thanks,
Thanks,
On 05/20, Hou Pengyang wrote:
This patches are to designed to optimize NAT/SIT flushing procedure:
patch 1) -- patch 3):
during flush_nat_entries, we do:
1) gang_lookup a radix tree, find all the dirty nat_entry_set;
2) sort nat_entry_set by nat_entry_set->entry_cnt, in order to
write to journal as much as possible to avoid unnessary IO.
This patch optimize the look_up & sort algorithm by introducing an array:
f2fs_nm_info->dirty_set[NAT_ENTRY_PER_BLOCK+1];
(struct list_head dirty_set[NAT_ENTRY_PER_BLOCK + 1])
dirty_set[1] links all nat_entry_set whose entry_cnt is 1
dirty_set[2] links all nat_entry_set whose entry_cnt is 2
......
dirty_set[N] links all nat_entry_set whose entry_cnt is N
as one NAT block has NAT_ENTRY_PER_BLOCK entries at MOST, so there should NOT
be one nat_entry_set whose entry_cnt is larger than NAT_ENTRY_PER_BLOCK.
So it is enough for f2fs_nm_info->dirty_set to link all nat_entry_sets in
system.
Update:
we update nat_entry_set in real-time, e.g originally
nat_entry_set->entry_cnt is
1, and licked by dirty_set[1]; then call __set_nat_cache_dirty to increase
nat_entry's
entry_cnt, we move this nat_entry_set ot dirty_set[2]'s tail, no need to
compare.
Flush:
when flush dirty nat_entry_set, we just flush nat_entry_set from
f2fs_nm_info->dirty_set[0] to f2fs_nm_info->dirty_set[NAT_ENTRY_PER_BLOCK],
where
gang_lookup and sort can be avoid.
footprint of this algorithm: sizeof(struct list_head)*NAT_ENTRY_PER_BLOCK
= 8*455 = 3.6k bytes
Same for SIT.
In patch 5), we use array to manage sit_entry_sets instead of list, which
can avoid list travel, and there is no need to alloc/free lab memory.
It is low footrpint consuming.
Hou Pengyang (5):
f2fs: use bucket sort to avoid tree lookup and list sort when nat flushing
f2fs: reconstruct sit flushing code
f2fs: use bucket sort to avoid list sort when flush sit entries
f2fs: avoid unnecessary to_journal checking
f2fs: use an array to record sit_entry_set info to make sort fast
fs/f2fs/f2fs.h | 5 +-
fs/f2fs/node.c | 79 ++++++++-----------
fs/f2fs/segment.c | 227 ++++++++++++++++++++++++++----------------------------
fs/f2fs/segment.h | 2 +-
4 files changed, 147 insertions(+), 166 deletions(-)
--
2.10.1
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