linux-kernel - RE: [Xen-devel] [PATCH 0/2] xen/blkback: Aggressively shrink page pools if a memory pressure is detected

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Date:   Wed, 4 Dec 2019 11:52:04 +0000
From:   "Durrant, Paul" <pdurrant@...zon.com>
To:     "Park, Seongjae" <sjpark@...zon.com>,
        "konrad.wilk@...cle.com" <konrad.wilk@...cle.com>,
        "roger.pau@...rix.com" <roger.pau@...rix.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>
CC:     "sj38.park@...il.com" <sj38.park@...il.com>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Park, Seongjae" <sjpark@...zon.com>
Subject: RE: [Xen-devel] [PATCH 0/2] xen/blkback: Aggressively shrink page
 pools if a memory pressure is detected

> -----Original Message-----
> From: Xen-devel <xen-devel-bounces@...ts.xenproject.org> On Behalf Of
> SeongJae Park
> Sent: 04 December 2019 11:34
> To: konrad.wilk@...cle.com; roger.pau@...rix.com; axboe@...nel.dk
> Cc: sj38.park@...il.com; xen-devel@...ts.xenproject.org; linux-
> block@...r.kernel.org; linux-kernel@...r.kernel.org; Park, Seongjae
> <sjpark@...zon.com>
> 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?

  Paul