linux-ext4 - Re: [PATCH 4/9] e2fsck: reduce memory usage for many directories

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Date:   Sat, 29 Feb 2020 18:29:14 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Andreas Dilger <adilger@...mcloud.com>
Cc:     linux-ext4@...r.kernel.org
Subject: Re: [PATCH 4/9] e2fsck: reduce memory usage for many directories

On Thu, Feb 06, 2020 at 06:09:41PM -0700, Andreas Dilger wrote:
> Pack struct dx_dir_info and dx_dirblock_info properly in memory, to
> avoid holes, and fields are not larger than necessary.  This reduces
> the memory needed for each hashed dir, according to pahole(1) from:
> 
>     struct dx_dir_info {
>         /* size: 32, cachelines: 1, members: 6 */
>         /* sum members: 26, holes: 1, sum holes: 2 */
>         /* padding: 4 */
>     };
>     struct dx_dirblock_info {
>         /* size: 56, cachelines: 1, members: 9 */
>         /* sum members: 48, holes: 2, sum holes: 8 */
>         /* last cacheline: 56 bytes */
>     };
> 
> to 8 bytes less for each directory and directory block, and leaves
> space for future use if needed (e.g. larger numblocks):
> 
>     struct dx_dir_info {
>         /* size: 24, cachelines: 1, members: 6 */
>         /* sum members: 20, holes: 1, sum holes: 4 */
>         /* bit holes: 1, sum bit holes: 7 bits */
>     };
>     struct dx_dirblock_info {
>         /* size: 48, cachelines: 1, members: 9 */
>     };
> 
> Signed-off-by: Andreas Dilger <adilger@...mcloud.com>
> Lustre-bug-id: https://jira.whamcloud.com/browse/LU-13197

Applied, thanks.

					- Ted