Linux-Block Archive on
 help / color / Atom feed
From: <>
To: "Durrant, Paul" <>,
	"" <>,
	"" <>,
	"" <>
Cc: "" <>,
	"" <>,
	"" <>,
	"" <>
Subject: Re: [Xen-devel] [PATCH 0/2] xen/blkback: Aggressively shrink page pools if a memory pressure is detected
Date: Wed, 4 Dec 2019 13:09:13 +0100
Message-ID: <> (raw)
In-Reply-To: <>

On 04.12.19 12:52, Durrant, Paul wrote:
>> -----Original Message-----
>> From: Xen-devel <> On Behalf Of
>> SeongJae Park
>> Sent: 04 December 2019 11:34
>> To:;;
>> Cc:;; linux-
>>;; Park, Seongjae
>> <>
>> Subject: [Xen-devel] [PATCH 0/2] xen/blkback: Aggressively shrink page
>> pools if a memory pressure is detected
>> Each `blkif` has a free pages pool for the grant mapping.  The size of
>> the pool starts from zero and be increased on demand while processing
>> the I/O requests.  If current I/O requests handling is finished or 100
>> milliseconds has passed since last I/O requests handling, it checks and
>> shrinks the pool to not exceed the size limit, `max_buffer_pages`.
>> Therefore, `blkfront` running guests can cause a memory pressure in the
>> `blkback` running guest by attaching arbitrarily large number of block
>> devices and inducing I/O.
> OOI... How do guests unilaterally cause the attachment of arbitrary numbers of PV devices?
Good point.  Many systems have their limit for the maximum number of the
devices.  Thus, 'arbitrarily' large number of devices cannot be attached.  So,
there is the upperbound.  System administrators might be able to avoid the
memory pressure problem by setting the limit low enough or giving more memory
to the 'blkback' running guest.

However, many systems also tempt to set the limit high enough so that guests
can satisfy and to give minimal memory to the 'blkback' running guest for cost

I believe this patchset can be helpful for such situations.

Anyway, using the term 'arbitrarily' is obvisously my fault.  I will update the
description in the next version of patchset.

SeongJae Park

>   Paul

      reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-04 11:34 SeongJae Park
2019-12-04 11:34 ` [PATCH 1/2] " SeongJae Park
2019-12-04 11:34 ` [PATCH 2/2] blkback: Add a module parameter for aggressive pool shrinking duration SeongJae Park
2019-12-04 11:52 ` [Xen-devel] [PATCH 0/2] xen/blkback: Aggressively shrink page pools if a memory pressure is detected Durrant, Paul
2019-12-04 12:09   ` sjpark [this message]

Reply instructions:

You may reply publically 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 \ \ \ \ \ \ \ \ \ \ \

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

Linux-Block Archive on

Archives are clonable:
	git clone --mirror linux-block/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-block linux-block/ \
	public-inbox-index linux-block

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone