linux-ext4 - Re: [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-Id: <81448013-525F-4C51-A9F3-88969CB49B70@gmail.com>
Date:   Fri, 24 Jul 2020 14:27:48 +0300
From:   Благодаренко Артём 
        <artem.blagodarenko@...il.com>
To:     Theodore Ts'o <tytso@....edu>
Cc:     Ext4 Developers List <linux-ext4@...r.kernel.org>,
        Alex Zhuravlev <bzzz@...mcloud.com>,
        Alex Zhuravlev <azhuravlev@...mcloud.com>,
        Andreas Dilger <adilger@...mcloud.com>
Subject: Re: [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning
 for good groups

Looks good.

Reviewed-by: Artem Blagodarenko <artem.blagodarenko@...il.com>

> On 17 Jul 2020, at 18:53, Theodore Ts'o <tytso@....edu> wrote:
> 
> From: Alex Zhuravlev <azhuravlev@...mcloud.com>
> 
> cr=0 is supposed to be an optimization to save CPU cycles, but if
> buddy data (in memory) is not initialized then all this makes no sense
> as we have to do sync IO taking a lot of cycles.  also, at cr=0
> mballoc doesn't store any avaibale chunk. cr=1 also skips groups using
> heuristic based on avg. fragment size. it's more useful to skip such
> groups and switch to cr=2 where groups will be scanned for available
> chunks.
> 
> using sparse image and dm-slow virtual device of 120TB was
> simulated. then the image was formatted and filled using debugfs to
> mark ~85% of available space as busy.  mount process w/o the patch
> couldn't complete in half an hour (according to vmstat it would take
> ~10-11 hours).  With the patch applied mount took ~20 seconds.
> 
> Lustre-bug-id: https://jira.whamcloud.com/browse/LU-12988
> Signed-off-by: Alex Zhuravlev <bzzz@...mcloud.com>
> Reviewed-by: Andreas Dilger <adilger@...mcloud.com>
> ---
> fs/ext4/mballoc.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 8a1e6e03c088..172994349bf6 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2195,7 +2195,18 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
> 
> 	/* We only do this if the grp has never been initialized */
> 	if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
> -		ret = ext4_mb_init_group(ac->ac_sb, group, GFP_NOFS);
> +		struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group,
> +								  NULL);
> +		int ret;
> +
> +		/* cr=0/1 is a very optimistic search to find large
> +		 * good chunks almost for free. if buddy data is
> +		 * not ready, then this optimization makes no sense */
> +		if (cr < 2 &&
> +		    !(ext4_has_group_desc_csum(sb) &&
> +		      (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))))
> +			return 0;
> +		ret = ext4_mb_init_group(sb, group, GFP_NOFS);
> 		if (ret)
> 			return ret;
> 	}
> -- 
> 2.24.1
>