From: "Michael S. Tsirkin" <mst@redhat.com>
To: Wei Wang <wei.w.wang@intel.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
Nitesh Narayan Lal <nitesh@redhat.com>,
kvm list <kvm@vger.kernel.org>,
David Hildenbrand <david@redhat.com>,
"Hansen, Dave" <dave.hansen@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm <linux-mm@kvack.org>,
Andrew Morton <akpm@linux-foundation.org>,
Yang Zhang <yang.zhang.wz@gmail.com>,
"pagupta@redhat.com" <pagupta@redhat.com>,
Rik van Riel <riel@surriel.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
"lcapitulino@redhat.com" <lcapitulino@redhat.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Paolo Bonzini <pbonzini@redhat.com>,
"Williams, Dan J" <dan.j.williams@intel.com>,
Alexander Duyck <alexander.h.duyck@linux.intel.com>
Subject: Re: use of shrinker in virtio balloon free page hinting
Date: Thu, 18 Jul 2019 01:58:16 -0400 [thread overview]
Message-ID: <20190718015319-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <5D300A32.4090300@intel.com>
On Thu, Jul 18, 2019 at 01:57:06PM +0800, Wei Wang wrote:
> On 07/18/2019 12:13 PM, Michael S. Tsirkin wrote:
> >
> > It makes sense for pages in the balloon (requested by hypervisor).
> > However free page hinting can freeze up lots of memory for its own
> > internal reasons. It does not make sense to ask hypervisor
> > to set flags in order to fix internal guest issues.
>
> Sounds reasonable to me. Probably we could move the flag check to
> shrinker_count and shrinker_scan as a reclaiming condition for
> ballooning pages only?
I think so, yes. I also wonder whether we should stop reporting
at that point - otherwise we'll just allocate the freed pages again.
>
> >
> > Right. But that does not include the pages in the hint vq,
> > which could be a significant amount of memory.
>
> I think it includes, as vb->num_free_page_blocks records the total number
> of free page blocks that balloon has taken from mm.
Oh - you are right. Thanks!
> For shrink_free_pages, it calls return_free_pages_to_mm, which pops pages
> from vb->free_page_list (this is the list where pages get enlisted after
> they
> are put to the hint vq, see get_free_page_and_send).
>
>
> >
> >
> > > > - if free pages are being reported, pages freed
> > > > by shrinker will just get re-allocated again
> > > fill_balloon will re-try the allocation after sleeping 200ms once allocation fails.
> > Even if ballon was never inflated, if shrinker frees some memory while
> > we are hinting, hint vq will keep going and allocate it back without
> > sleeping.
>
> Still see get_free_page_and_send. -EINTR is returned when page allocation
> fails,
> and reporting ends then.
what if it does not fail?
>
> Shrinker is called on system memory pressure. On memory pressure
> get_free_page_and_send will fail memory allocation, so it stops allocating
> more.
Memory pressure could be triggered by an unrelated allocation
e.g. from another driver.
>
>
> Best,
> Wei
next prev parent reply other threads:[~2019-07-18 5:58 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 11:20 use of shrinker in virtio balloon free page hinting Michael S. Tsirkin
2019-07-17 11:32 ` David Hildenbrand
2019-07-17 14:10 ` David Hildenbrand
2019-07-17 14:34 ` Michael S. Tsirkin
2019-07-17 14:38 ` David Hildenbrand
2019-07-17 15:46 ` Wang, Wei W
2019-07-18 4:13 ` Michael S. Tsirkin
2019-07-18 5:57 ` Wei Wang
2019-07-18 5:58 ` Michael S. Tsirkin [this message]
2019-07-18 6:30 ` Wei Wang
2019-07-18 6:47 ` Michael S. Tsirkin
2019-07-18 9:08 ` Wei Wang
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