Re: [PATCH v2 6/6] iomap: reduce unnecessary state_lock when setting ifs uptodate and dirty bits

Zhang Yi
2024-08-13T08:15:41Z

On 2024/8/13 1:00, Matthew Wilcox wrote:
> On Mon, Aug 12, 2024 at 08:11:59PM +0800, Zhang Yi wrote:
>> @@ -866,9 +899,8 @@ static bool __iomap_write_end(struct inode *inode, loff_t pos, size_t len,
>> */
>> if (unlikely(copied < len && !folio_test_uptodate(folio)))
>> return false;
>> - iomap_set_range_uptodate(folio, offset_in_folio(folio, pos), len);
>> - iomap_set_range_dirty(folio, offset_in_folio(folio, pos), copied);
>> - filemap_dirty_folio(inode->i_mapping, folio);
>> +
>> + iomap_set_range_dirty_uptodate(folio, from, copied);
>> return true;
>
> I wonder how often we overwrite a completely uptodate folio rather than
> writing new data to a fresh folio? iow, would this be a measurable
> optimisation?
>
> if (folio_test_uptodate(folio))
> iomap_set_range_dirty(folio, from, copied);
> else
> iomap_set_range_dirty_uptodate(folio, from, copied);
>

Thanks for the suggestion, I'm not sure how often as well, but I suppose
we could do this optimisation since I've tested it and found this is
harmless for the case of writing new data to a fresh folio. However, this
can further improves the overwrite performance, the UnixBench tests result
shows the performance gain can be increased to about ~15% on my machine
with 50GB ramdisk and xfs filesystem.

UnixBench test cmd:
./Run -i 1 -c 1 fstime-w

Base:
x86 File Write 1024 bufsize 2000 maxblocks 524708.0 KBps
arm64 File Write 1024 bufsize 2000 maxblocks 801965.0 KBps

After this series:
x86 File Write 1024 bufsize 2000 maxblocks 569218.0 KBps
arm64 File Write 1024 bufsize 2000 maxblocks 871605.0 KBps

After this measurable optimisation:
x86 File Write 1024 bufsize 2000 maxblocks 609620.0 KBps
arm64 File Write 1024 bufsize 2000 maxblocks 910534.0 KBps

Thanks,
Yi.