linux-ext4 - Re: [PATCH] ext4: Avoid unnecessary transaction starts during writeback

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Message-ID: <20200529031925.GL228632@mit.edu>
Date:   Thu, 28 May 2020 23:19:25 -0400
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Jan Kara <jack@...e.cz>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: Avoid unnecessary transaction starts during
 writeback

On Mon, May 25, 2020 at 10:12:15AM +0200, Jan Kara wrote:
> ext4_writepages() currently works in a loop like:
>   start a transaction
>   scan inode for pages to write
>   map and submit these pages
>   stop the transaction
> 
> This loop results in starting transaction once more than is needed
> because in the last iteration we start a transaction only to scan the
> inode and find there are no pages to write. This can be significant
> increase in number of transaction starts for single-extent files or
> files that have all blocks already mapped. Furthermore we already know
> from previous iteration whether there are more pages to write or not. So
> propagate the information from mpage_prepare_extent_to_map() and avoid
> unnecessary looping in case there are no more pages to write.
> 
> Signed-off-by: Jan Kara <jack@...e.cz>

Thanks, applied.  I like how it shrinks the source file.  :-)

		    	     		- Ted