linux-ext4 - Re: [PATCH] ext4: Improve write performance with disabled delalloc

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Message-Id: <165551818831.612215.11479154639163365692.b4-ty@mit.edu>
Date:   Fri, 17 Jun 2022 22:12:05 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     "Theodore Ts'o" <tytso@....edu>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Improve write performance with disabled delalloc

On Fri, 20 May 2022 13:14:02 +0200, Jan Kara wrote:
> When delayed allocation is disabled (either through mount option or
> because we are running low on free space), ext4_write_begin() allocates
> blocks with EXT4_GET_BLOCKS_IO_CREATE_EXT flag. With this flag extent
> merging is disabled and since ext4_write_begin() is called for each page
> separately, we end up with a *lot* of 1 block extents in the extent tree
> and following writeback is writing 1 block at a time which results in
> very poor write throughput (4 MB/s instead of 200 MB/s). These days when
> ext4_get_block_unwritten() is used only by ext4_write_begin(),
> ext4_page_mkwrite() and inline data conversion, we can safely allow
> extent merging to happen from these paths since following writeback will
> happen on different boundaries anyway. So use
> EXT4_GET_BLOCKS_CREATE_UNRIT_EXT instead which restores the performance.
> 
> [...]

Applied, thanks!

[1/1] ext4: Improve write performance with disabled delalloc
      commit: 8d5459c11f548131ce48b2fbf45cccc5c382558f

Best regards,
-- 
Theodore Ts'o <tytso@....edu>