LKML Archive on
help / color / mirror / Atom feed
From: Jens Axboe <>
To: Paolo Valente <>
Subject: Re: [PATCH BUGFIX 1/1] block, bfq: honor already-setup queue merges
Date: Thu, 2 Sep 2021 06:37:16 -0600	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 8/2/21 8:13 AM, Paolo Valente wrote:
> The function bfq_setup_merge prepares the merging between two
> bfq_queues, say bfqq and new_bfqq. To this goal, it assigns
> bfqq->new_bfqq = new_bfqq. Then, each time some I/O for bfqq arrives,
> the process that generated that I/O is disassociated from bfqq and
> associated with new_bfqq (merging is actually a redirection). In this
> respect, bfq_setup_merge increases new_bfqq->ref in advance, adding
> the number of processes that are expected to be associated with
> new_bfqq.
> Unfortunately, the stable-merging mechanism interferes with this
> setup. After bfqq->new_bfqq has been set by bfq_setup_merge, and
> before all the expected processes have been associated with
> bfqq->new_bfqq, bfqq may happen to be stably merged with a different
> queue than the current bfqq->new_bfqq. In this case, bfqq->new_bfqq
> gets changed. So, some of the processes that have been already
> accounted for in the ref counter of the previous new_bfqq will not be
> associated with that queue.  This creates an unbalance, because those
> references will never be decremented.
> This commit fixes this issue by reestablishing the previous, natural
> behaviour: once bfqq->new_bfqq has been set, it will not be changed
> until all expected redirections have occurred.

Applied, thanks.

Jens Axboe

      parent reply	other threads:[~2021-09-02 12:37 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-02 14:13 [PATCH BUGFIX 0/1] block, bfq: fix a bug causing a memory leak Paolo Valente
2021-08-02 14:13 ` [PATCH BUGFIX 1/1] block, bfq: honor already-setup queue merges Paolo Valente
2021-08-26  9:16   ` Paolo Valente
2021-09-02  7:32     ` Paolo Valente
2021-09-02 12:37   ` Jens Axboe [this message]

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:

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

  git send-email \ \ \ \ \ \ \
    --subject='Re: [PATCH BUGFIX 1/1] block, bfq: honor already-setup queue merges' \

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

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).