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From: Mel Gorman <mgorman@techsingularity.net>
To: David Hildenbrand <david@redhat.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>,
	kvm@vger.kernel.org, mst@redhat.com,
	linux-kernel@vger.kernel.org, willy@infradead.org,
	mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org,
	vbabka@suse.cz, yang.zhang.wz@gmail.com, nitesh@redhat.com,
	konrad.wilk@oracle.com, pagupta@redhat.com, riel@surriel.com,
	lcapitulino@redhat.com, dave.hansen@intel.com,
	wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com,
	dan.j.williams@intel.com, alexander.h.duyck@linux.intel.com,
	osalvador@suse.de
Subject: Re: [PATCH v15 0/7] mm / virtio: Provide support for free page reporting
Date: Fri, 13 Dec 2019 11:08:06 +0000	[thread overview]
Message-ID: <20191213110806.GA3178@techsingularity.net> (raw)
In-Reply-To: <ead08075-c886-dc7d-2c7b-47b20e00b515@redhat.com>

On Fri, Dec 13, 2019 at 11:00:42AM +0100, David Hildenbrand wrote:
> > A brief history on the background of free page reporting can be found at:
> > https://lore.kernel.org/lkml/29f43d5796feed0dec8e8bb98b187d9dac03b900.camel@linux.intel.com/
> > 
> > Changes from v13:
> > https://lore.kernel.org/lkml/20191105215940.15144.65968.stgit@localhost.localdomain/
> > Rewrote core reporting functionality
> >   Merged patches 3 & 4
> >   Dropped boundary list and related code
> >   Folded get_reported_page into page_reporting_fill
> >   Folded page_reporting_fill into page_reporting_cycle
> > Pulled reporting functionality out of free_reported_page
> >   Renamed it to __free_isolated_page
> >   Moved page reporting specific bits to page_reporting_drain
> > Renamed phdev to prdev since we aren't "hinting" we are "reporting"
> > Added documentation to describe the usage of unused page reporting
> > Updated cover page and patch descriptions to avoid mention of boundary
> > 
> > Changes from v14:
> > https://lore.kernel.org/lkml/20191119214454.24996.66289.stgit@localhost.localdomain/
> > Renamed "unused page reporting" to "free page reporting"
> >   Updated code, kconfig, and patch descriptions
> > Split out patch for __free_isolated_page
> >   Renamed function to __putback_isolated_page
> > Rewrote core reporting functionality
> >   Added logic to reschedule worker in 2 seconds instead of run to completion
> >   Removed reported_pages statistics
> >   Removed REPORTING_REQUESTED bit used in zone flags
> >   Replaced page_reporting_dev_info refcount with state variable
> >   Removed scatterlist from page_reporting_dev_info
> >   Removed capacity from page reporting device
> >   Added dynamic scatterlist allocation/free at start/end of reporting process
> >   Updated __free_one_page so that reported pages are not always added to tail
> >   Added logic to handle error from report function
> > Updated virtio-balloon patch that adds support for page reporting
> >   Updated patch description to try and highlight differences in approaches
> >   Updated logic to reflect that we cannot limit the scatterlist from device
> 
> Last time Mel said
> 
> "Ok, I'm ok with how this hooks into the allocator as the overhead is
> minimal. However, the patch itself still includes a number of
> optimisations instead of being a bare-boned implementation of the
> feature with optimisations layered on top."
> 

I didn't get the chance to take a close look as I'm trying to clear as
much as possible from my table on the run-up to Christmas so I don't come
back to a disaster inbox. I also noted that the Acks for earlier patches
were not included so I was uncertain if doing a full review would still
be a good use of time when time was tight.

That said, some optimisations are still included but much reduced. For
example, list rotations are still there but it's very straight-forward.
The refcount is gone which is good and replaced by a state, which could be
be better documented, but is more straight forward and the zone->lock is
back protecting the free lists primarily and not zone metadata or prdev
metadata (at least not obviously). I didn't put in the time to see if
the atomic_set in page_reporting_process() is ok or whether state could
be lost but I *think* it's ok because it should be called from just one
workqueue request and they shouldn't be stacked. A comment there explaining
why atomic_set is definitely correct would be helpful.

I'm inclined to decide that yes, this version is potentially ok as a
bare minimum but didn't put in the time to be 100% sure.
 
-- 
Mel Gorman
SUSE Labs

  reply	other threads:[~2019-12-13 20:36 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-05 16:22 Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 1/7] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 2/7] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 3/7] mm: Add function __putback_isolated_page Alexander Duyck
2019-12-16 11:36   ` David Hildenbrand
2019-12-16 16:22     ` Alexander Duyck
2019-12-17 10:58       ` David Hildenbrand
2019-12-17 16:26         ` Alexander Duyck
2019-12-17 17:24           ` David Hildenbrand
2019-12-17 18:24             ` Alexander Duyck
2019-12-17 18:46               ` David Hildenbrand
2019-12-17 21:50                 ` Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 4/7] mm: Introduce Reported pages Alexander Duyck
2019-12-16 10:17   ` Nitesh Narayan Lal
2019-12-16 16:28     ` Alexander Duyck
2019-12-17  8:55       ` Nitesh Narayan Lal
2019-12-17 16:31         ` Alexander Duyck
2019-12-18  7:31           ` Mel Gorman
2019-12-16 11:44   ` Nitesh Narayan Lal
2019-12-16 16:10     ` Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 5/7] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-12-13  7:03   ` Michael S. Tsirkin
2019-12-05 16:22 ` [PATCH v15 6/7] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
2019-12-13  7:08   ` Michael S. Tsirkin
2019-12-13 16:35     ` Alexander Duyck
2019-12-15  9:29       ` Michael S. Tsirkin
2019-12-13 10:15   ` David Hildenbrand
2019-12-13 16:37     ` Alexander Duyck
2019-12-05 16:23 ` [PATCH v15 7/7] mm: Add free page reporting documentation Alexander Duyck
2019-12-05 16:24 ` [PATCH v15 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2019-12-05 16:24 ` [PATCH v15 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
2019-12-05 16:24 ` [PATCH v15 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
2019-12-05 16:26 ` [PATCH v15 QEMU 4/3 RFC] memory: Add support for MADV_FREE as mechanism to lazy discard pages Alexander Duyck
2019-12-12 23:47 ` [PATCH v15 0/7] mm / virtio: Provide support for free page reporting Alexander Duyck
2019-12-13 10:00 ` David Hildenbrand
2019-12-13 11:08   ` Mel Gorman [this message]
2019-12-13 16:59     ` Alexander Duyck
2019-12-13 16:46   ` Alexander Duyck
2019-12-16 12:21     ` David Hildenbrand

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