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From: "Wang, Wei W" <wei.w.wang@intel.com>
To: David Hildenbrand <david@redhat.com>,
	Tyler Sanderson <tysand@google.com>
Cc: "virtualization@lists.linux-foundation.org"
	<virtualization@lists.linux-foundation.org>,
	David Rientjes <rientjes@google.com>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Michael S. Tsirkin" <mst@redhat.com>
Subject: RE: Balloon pressuring page cache
Date: Thu, 30 Jan 2020 15:31:09 +0000	[thread overview]
Message-ID: <286AC319A985734F985F78AFA26841F73E3F8A02@shsmsx102.ccr.corp.intel.com> (raw)
In-Reply-To: <75d4594f-0864-5172-a0f8-f97affedb366@redhat.com>

On Thursday, January 30, 2020 11:03 PM, David Hildenbrand wrote:
> On 29.01.20 20:11, Tyler Sanderson wrote:
> >
> >
> > On Wed, Jan 29, 2020 at 2:31 AM David Hildenbrand <david@redhat.com
> > <mailto:david@redhat.com>> wrote:
> >
> >     On 29.01.20 01:22, Tyler Sanderson via Virtualization wrote:
> >     > A primary advantage of virtio balloon over other memory reclaim
> >     > mechanisms is that it can pressure the guest's page cache into
> >     shrinking.
> >     >
> >     > However, since the balloon driver changed to using the shrinker API
> >     >
> >
> <https://github.com/torvalds/linux/commit/71994620bb25a8b109388fefa9
> e99a28e355255a#diff-fd202acf694d9eba19c8c64da3e480c9> this
> >     > use case has become a bit more tricky. I'm wondering what the
> intended
> >     > device implementation is.
> >     >
> >     > When inflating the balloon against page cache (i.e. no free memory
> >     > remains) vmscan.c will both shrink page cache, but also invoke the
> >     > shrinkers -- including the balloon's shrinker. So the balloon driver
> >     > allocates memory which requires reclaim, vmscan gets this memory
> by
> >     > shrinking the balloon, and then the driver adds the memory back to
> the
> >     > balloon. Basically a busy no-op.

Per my understanding, the balloon allocation won’t invoke shrinker as __GFP_DIRECT_RECLAIM isn't set, no?


> >     >
> >     > If file IO is ongoing during this balloon inflation then the page
> >     cache
> >     > could be growing which further puts "back pressure" on the balloon
> >     > trying to inflate. In testing I've seen periods of > 45 seconds where
> >     > balloon inflation makes no net forward progress.

I think this is intentional (but could be improved). As inflation does not stop when the allocation fails (it simply sleeps for a while and resumes.. repeat till there are memory to inflate)
That's why you see no inflation progress for long time under memory pressure.


Best,
Wei

  parent reply	other threads:[~2020-01-30 15:38 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CAJuQAmpDUyve2S+oxp9tLUhuRcnddXnNztC5PmYOOCpY6c68xg@mail.gmail.com>
     [not found] ` <91270a68-ff48-88b0-219c-69801f0c252f@redhat.com>
     [not found]   ` <CAJuQAmoaK0Swytu2Os_SQRfG5_LqiCPaDa9yatatm9MtfncNTQ@mail.gmail.com>
2020-01-30 15:02     ` Balloon pressuring page cache David Hildenbrand
2020-01-30 15:20       ` Michael S. Tsirkin
2020-01-30 15:23         ` David Hildenbrand
2020-01-30 15:31       ` Wang, Wei W [this message]
2020-01-30 19:59         ` Tyler Sanderson
2020-02-03 13:11           ` Michael S. Tsirkin
2020-02-03 16:18             ` Alexander Duyck
2020-02-03 16:34               ` David Hildenbrand
2020-02-03 17:03                 ` Michael S. Tsirkin
2020-02-03 20:32                   ` Tyler Sanderson
2020-02-03 21:22                     ` Alexander Duyck
2020-02-03 23:16                       ` Tyler Sanderson
2020-02-04  0:10                         ` Alexander Duyck
2020-02-04  5:45                     ` Michael S. Tsirkin
2020-02-04  8:29                     ` David Hildenbrand
2020-02-04 18:52                       ` Tyler Sanderson
2020-02-04 18:56                         ` Michael S. Tsirkin
2020-02-04 19:17                         ` David Hildenbrand
2020-02-04 23:58                           ` Tyler Sanderson
2020-02-05  0:15                             ` Tyler Sanderson
2020-02-05  6:57                             ` Michael S. Tsirkin
2020-02-05 19:01                               ` Tyler Sanderson
2020-02-05 19:22                                 ` Alexander Duyck
2020-02-05 21:44                                   ` Tyler Sanderson
2020-02-06 11:00                                     ` David Hildenbrand
2020-02-03 22:50                 ` Nadav Amit
2020-02-04  8:35                   ` David Hildenbrand
2020-02-04  8:40                     ` Michael S. Tsirkin
2020-02-04  8:48                       ` David Hildenbrand
2020-02-04 14:30                       ` David Hildenbrand
2020-02-04 16:50                         ` Michael S. Tsirkin
2020-02-04 16:56                           ` David Hildenbrand
2020-02-04 20:33                             ` Michael S. Tsirkin
2020-02-05  8:31                               ` David Hildenbrand
2020-02-05  6:52                           ` Wang, Wei W
2020-02-05  7:05                             ` Michael S. Tsirkin
2020-02-05  8:50                               ` Wang, Wei W
2020-02-05  6:49                         ` Wang, Wei W
2020-02-05  8:19                           ` David Hildenbrand
2020-02-05  8:54                             ` Wang, Wei W
2020-02-05  8:56                               ` David Hildenbrand
2020-02-05  9:00                                 ` Wang, Wei W
2020-02-05  9:05                                   ` David Hildenbrand
2020-02-05  9:19                                     ` Wang, Wei W
2020-02-05  9:22                                       ` David Hildenbrand
2020-02-05  9:35                                         ` Wang, Wei W
2020-02-05  9:37                                           ` David Hildenbrand
2020-02-05  9:49                                             ` Wang, Wei W
2020-02-05  9:58                                               ` David Hildenbrand
2020-02-05 10:25                                                 ` Michael S. Tsirkin
2020-02-05 10:42                                                   ` David Hildenbrand
2020-02-05  9:35                                         ` Michael S. Tsirkin
2020-02-05 18:43                                   ` Tyler Sanderson
2020-02-06  9:30                                     ` Wang, Wei W
2020-02-05  7:35                   ` Nadav Amit
2020-02-05  8:19                     ` David Hildenbrand
2020-02-05 10:27                       ` Michael S. Tsirkin
2020-02-05 10:43                         ` David Hildenbrand
2020-01-30 22:46       ` Tyler Sanderson

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