From: Brian Foster <bfoster@redhat.com>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 15/24] xfs: eagerly free shadow buffers to reduce CIL footprint
Date: Mon, 5 Aug 2019 14:03:01 -0400 [thread overview]
Message-ID: <20190805180300.GE14760@bfoster> (raw)
In-Reply-To: <20190801021752.4986-16-david@fromorbit.com>
On Thu, Aug 01, 2019 at 12:17:43PM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> The CIL can pin a lot of memory and effectively defines the lower
> free memory boundary of operation for XFS. The way we hang onto
> log item shadow buffers "just in case" effectively doubles the
> memory footprint of the CIL for dubious reasons.
>
> That is, we hang onto the old shadow buffer in case the next time
> we log the item it will fit into the shadow buffer and we won't have
> to allocate a new one. However, we only ever tend to grow dirty
> objects in the CIL through relogging, so once we've allocated a
> larger buffer the old buffer we set as a shadow buffer will never
> get reused as the amount we log never decreases until the item is
> clean. And then for buffer items we free the log item and the shadow
> buffers, anyway. Inode items will hold onto their shadow buffer
> until they are reclaimed - this could double the inode's memory
> footprint for it's lifetime...
>
> Hence we should just free the old log item buffer when we replace it
> with a new shadow buffer rather than storing it for later use. It's
> not useful, get rid of it as early as possible.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_log_cil.c | 7 +++----
> 1 file changed, 3 insertions(+), 4 deletions(-)
>
> diff --git a/fs/xfs/xfs_log_cil.c b/fs/xfs/xfs_log_cil.c
> index fa5602d0fd7f..1863a9bdf4a9 100644
> --- a/fs/xfs/xfs_log_cil.c
> +++ b/fs/xfs/xfs_log_cil.c
> @@ -238,9 +238,7 @@ xfs_cil_prepare_item(
> /*
> * If there is no old LV, this is the first time we've seen the item in
> * this CIL context and so we need to pin it. If we are replacing the
> - * old_lv, then remove the space it accounts for and make it the shadow
> - * buffer for later freeing. In both cases we are now switching to the
> - * shadow buffer, so update the the pointer to it appropriately.
> + * old_lv, then remove the space it accounts for and free it.
> */
The comment above xlog_cil_alloc_shadow_bufs() needs a similar update
around how we handle the old buffer when the shadow buffer is used.
> if (!old_lv) {
> if (lv->lv_item->li_ops->iop_pin)
> @@ -251,7 +249,8 @@ xfs_cil_prepare_item(
>
> *diff_len -= old_lv->lv_bytes;
> *diff_iovecs -= old_lv->lv_niovecs;
> - lv->lv_item->li_lv_shadow = old_lv;
> + kmem_free(old_lv);
> + lv->lv_item->li_lv_shadow = NULL;
> }
So IIUC this is the case where we allocated a shadow buffer, the item
was already pinned (so old_lv is still around) but we ended up using the
shadow buffer for this relog. Instead of keeping the old buffer around
as a new shadow, we toss it. That makes sense, but if the objective is
to not leave dangling shadow buffers around as such, what about the case
where we allocated a shadow buffer but didn't end up using it because
old_lv was reusable? It looks like we still keep the shadow buffer
around in that scenario with a similar lifetime as the swapout scenario
this patch removes. Hm?
Brian
>
> /* attach new log vector to log item */
> --
> 2.22.0
>
next prev parent reply other threads:[~2019-08-05 18:03 UTC|newest]
Thread overview: 87+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-01 2:17 [RFC] [PATCH 00/24] mm, xfs: non-blocking inode reclaim Dave Chinner
2019-08-01 2:17 ` [PATCH 01/24] mm: directed shrinker work deferral Dave Chinner
2019-08-02 15:27 ` Brian Foster
2019-08-04 1:49 ` Dave Chinner
2019-08-05 17:42 ` Brian Foster
2019-08-05 23:43 ` Dave Chinner
2019-08-06 12:27 ` Brian Foster
2019-08-06 22:22 ` Dave Chinner
2019-08-07 11:13 ` Brian Foster
2019-08-01 2:17 ` [PATCH 02/24] shrinkers: use will_defer for GFP_NOFS sensitive shrinkers Dave Chinner
2019-08-02 15:27 ` Brian Foster
2019-08-04 1:50 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 03/24] mm: factor shrinker work calculations Dave Chinner
2019-08-02 15:08 ` Nikolay Borisov
2019-08-04 2:05 ` Dave Chinner
2019-08-02 15:31 ` Brian Foster
2019-08-01 2:17 ` [PATCH 04/24] shrinker: defer work only to kswapd Dave Chinner
2019-08-02 15:34 ` Brian Foster
2019-08-04 16:48 ` Nikolay Borisov
2019-08-04 21:37 ` Dave Chinner
2019-08-07 16:12 ` kbuild test robot
2019-08-07 18:00 ` kbuild test robot
2019-08-01 2:17 ` [PATCH 05/24] shrinker: clean up variable types and tracepoints Dave Chinner
2019-08-01 2:17 ` [PATCH 06/24] mm: reclaim_state records pages reclaimed, not slabs Dave Chinner
2019-08-01 2:17 ` [PATCH 07/24] mm: back off direct reclaim on excessive shrinker deferral Dave Chinner
2019-08-01 2:17 ` [PATCH 08/24] mm: kswapd backoff for shrinkers Dave Chinner
2019-08-01 2:17 ` [PATCH 09/24] xfs: don't allow log IO to be throttled Dave Chinner
2019-08-01 13:39 ` Chris Mason
2019-08-01 23:58 ` Dave Chinner
2019-08-02 8:12 ` Christoph Hellwig
2019-08-02 14:11 ` Chris Mason
2019-08-02 18:34 ` Matthew Wilcox
2019-08-02 23:28 ` Dave Chinner
2019-08-05 18:32 ` Chris Mason
2019-08-05 23:09 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 10/24] xfs: fix missed wakeup on l_flush_wait Dave Chinner
2019-08-01 2:17 ` [PATCH 11/24] xfs:: account for memory freed from metadata buffers Dave Chinner
2019-08-01 8:16 ` Christoph Hellwig
2019-08-01 9:21 ` Dave Chinner
2019-08-06 5:51 ` Christoph Hellwig
2019-08-01 2:17 ` [PATCH 12/24] xfs: correctly acount for reclaimable slabs Dave Chinner
2019-08-06 5:52 ` Christoph Hellwig
2019-08-06 21:05 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 13/24] xfs: synchronous AIL pushing Dave Chinner
2019-08-05 17:51 ` Brian Foster
2019-08-05 23:21 ` Dave Chinner
2019-08-06 12:29 ` Brian Foster
2019-08-01 2:17 ` [PATCH 14/24] xfs: tail updates only need to occur when LSN changes Dave Chinner
2019-08-05 17:53 ` Brian Foster
2019-08-05 23:28 ` Dave Chinner
2019-08-06 5:33 ` Dave Chinner
2019-08-06 12:53 ` Brian Foster
2019-08-06 21:11 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 15/24] xfs: eagerly free shadow buffers to reduce CIL footprint Dave Chinner
2019-08-05 18:03 ` Brian Foster [this message]
2019-08-05 23:33 ` Dave Chinner
2019-08-06 12:57 ` Brian Foster
2019-08-06 21:21 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 16/24] xfs: Lower CIL flush limit for large logs Dave Chinner
2019-08-04 17:12 ` Nikolay Borisov
2019-08-01 2:17 ` [PATCH 17/24] xfs: don't block kswapd in inode reclaim Dave Chinner
2019-08-06 18:21 ` Brian Foster
2019-08-06 21:27 ` Dave Chinner
2019-08-07 11:14 ` Brian Foster
2019-08-01 2:17 ` [PATCH 18/24] xfs: reduce kswapd blocking on inode locking Dave Chinner
2019-08-06 18:22 ` Brian Foster
2019-08-06 21:33 ` Dave Chinner
2019-08-07 11:30 ` Brian Foster
2019-08-07 23:16 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 19/24] xfs: kill background reclaim work Dave Chinner
2019-08-01 2:17 ` [PATCH 20/24] xfs: use AIL pushing for inode reclaim IO Dave Chinner
2019-08-07 18:09 ` Brian Foster
2019-08-07 23:10 ` Dave Chinner
2019-08-08 16:20 ` Brian Foster
2019-08-01 2:17 ` [PATCH 21/24] xfs: remove mode from xfs_reclaim_inodes() Dave Chinner
2019-08-01 2:17 ` [PATCH 22/24] xfs: track reclaimable inodes using a LRU list Dave Chinner
2019-08-08 16:36 ` Brian Foster
2019-08-09 0:10 ` Dave Chinner
2019-08-01 2:17 ` [PATCH 23/24] xfs: reclaim inodes from the LRU Dave Chinner
2019-08-08 16:39 ` Brian Foster
2019-08-09 1:20 ` Dave Chinner
2019-08-09 12:36 ` Brian Foster
2019-08-11 2:17 ` Dave Chinner
2019-08-11 12:46 ` Brian Foster
2019-08-01 2:17 ` [PATCH 24/24] xfs: remove unusued old inode reclaim code Dave Chinner
2019-08-06 5:57 ` [RFC] [PATCH 00/24] mm, xfs: non-blocking inode reclaim Christoph Hellwig
2019-08-06 21:37 ` Dave Chinner
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=20190805180300.GE14760@bfoster \
--to=bfoster@redhat.com \
--cc=david@fromorbit.com \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=linux-xfs@vger.kernel.org \
/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
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).