Linux-ext4 Archive on lore.kernel.org
 help / color / Atom feed
From: Andreas Dilger <adilger@dilger.ca>
To: Theodore Ts'o <tytso@mit.edu>
Cc: Ext4 Developers List <linux-ext4@vger.kernel.org>,
	Alex Zhuravlev <azhuravlev@whamcloud.com>,
	Artem Blagodarenko <artem.blagodarenko@gmail.com>
Subject: Re: [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups
Date: Sat, 1 Aug 2020 02:49:12 -0600
Message-ID: <79A96A07-ECA0-410A-8775-457B9C3CFFF1@dilger.ca> (raw)
In-Reply-To: <20200731190805.181253-3-tytso@mit.edu>


[-- Attachment #1: Type: text/plain, Size: 2936 bytes --]


> On Jul 31, 2020, at 1:08 PM, Theodore Ts'o <tytso@mit.edu> wrote:
> 
> From: Alex Zhuravlev <azhuravlev@whamcloud.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 choose any avaibale chunk.  cr=1 also skips groups

(typo) "available"

> 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.  However, we always read the first block group in a
> flex_bg so metadata blocks will get read into the first flex_bg if
> possible.
> 
> 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 <azhuravlev@whamcloud.com>
> Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
> Reviewed-by: Artem Blagodarenko <artem.blagodarenko@gmail.com>

Looks good, one trivial cleanup below could also be done before landing.

> ---
> fs/ext4/mballoc.c | 22 +++++++++++++++++++++-
> 1 file changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index fcc702f1ff15..b1ef35a9e9f1 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -2195,7 +2196,26 @@ 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.  But
> +		 * we never skip the first block group in a flex_bg,
> +		 * since this gets used for metadata block allocation,
> +		 * and we want to make sure we locate metadata blocks
> +		 * in the first block group in the flex_bg if
> +		 * possible.

(style) "possible" could fit on the previous line?

> +		 */
> +		if (cr < 2 &&
> +		    (!sbi->s_log_groups_per_flex ||
> +		     ((group & ((1 << sbi->s_log_groups_per_flex) - 1)) != 0)) &&
> +		    !(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
> 


Cheers, Andreas






[-- Attachment #2: Message signed with OpenPGP --]
[-- Type: application/pgp-signature, Size: 873 bytes --]

  reply index

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31 19:08 [PATCH 0/4] V2- ext4 block bitmap prefetch patches Theodore Ts'o
2020-07-31 19:08 ` [PATCH 1/4] ext4: add prefetching for block allocation bitmaps Theodore Ts'o
2020-07-31 19:08 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o
2020-08-01  8:49   ` Andreas Dilger [this message]
2020-07-31 19:08 ` [PATCH 3/4] ext4: indicate via a block bitmap read is prefetched via a tracepoint Theodore Ts'o
2020-07-31 19:08 ` [PATCH 4/4] ext4: add prefetch_block_bitmaps mount options Theodore Ts'o
2020-08-01  8:57   ` Andreas Dilger
  -- strict thread matches above, loose matches on Subject: below --
2020-07-17 15:53 [PATCH 0/4] ex4 block bitmap prefetching Theodore Ts'o
2020-07-17 15:53 ` [PATCH 2/4] ext4: skip non-loaded groups at cr=0/1 when scanning for good groups Theodore Ts'o
2020-07-21  7:48   ` Andreas Dilger
2020-07-24 11:27   ` Благодаренко Артём

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=79A96A07-ECA0-410A-8775-457B9C3CFFF1@dilger.ca \
    --to=adilger@dilger.ca \
    --cc=artem.blagodarenko@gmail.com \
    --cc=azhuravlev@whamcloud.com \
    --cc=linux-ext4@vger.kernel.org \
    --cc=tytso@mit.edu \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-ext4 Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-ext4/0 linux-ext4/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-ext4 linux-ext4/ https://lore.kernel.org/linux-ext4 \
		linux-ext4@vger.kernel.org
	public-inbox-index linux-ext4

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-ext4


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git