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From: David Hildenbrand <david@redhat.com>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>,
	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,
	mgorman@techsingularity.net, 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, osalvador@suse.de
Subject: Re: [PATCH v15 3/7] mm: Add function __putback_isolated_page
Date: Tue, 17 Dec 2019 19:46:47 +0100	[thread overview]
Message-ID: <08EFF184-E727-4A79-ABEF-52F2463860C3@redhat.com> (raw)
In-Reply-To: <1a6e4646f570bf193924e099557841eb6e77a80d.camel@linux.intel.com>



> Am 17.12.2019 um 19:25 schrieb Alexander Duyck <alexander.h.duyck@linux.intel.com>:
> 
> On Tue, 2019-12-17 at 18:24 +0100, David Hildenbrand wrote:
>>>>> Also there are some scenarios where __page_to_pfn is not that simple a
>>>>> call with us having to get the node ID so we can find the pgdat structure
>>>>> to perform the calculation. I'm not sure the compiler would be ble to
>>>>> figure out that the result is the same for both calls, so it is better to
>>>>> make it explicit.
>>>> 
>>>> Only in case of CONFIG_SPARSEMEM we have to go via the section - but I
>>>> doubt this is really worth optimizing here.
>>>> 
>>>> But yeah, I'm fine with this change, only "IMHO
>>>> get_pageblock_migratetype() would be nicer" :)
>>> 
>>> Aren't most distros running with CONFIG_SPARSEMEM enabled? If that is the
>>> case why not optimize for it?
>> 
>> Because I tend to dislike micro-optimizations without performance
>> numbers for code that is not on a hot path. But I mean in this case, as
>> you said, you need the pfn either way, so it's completely fine with.
>> 
>> I do wonder, however, if you should just pass in the migratetype from
>> the caller. That would be even faster ;)
> 
> The problem is page isolation. We can end up with a page being moved to an
> isolate pageblock while we aren't holding the zone lock, and as such we
> likely need to test it again anyway. So there isn't value in storing and
> reusing the value for cases like page reporting.
> 
> In addition, the act of isolating the page can cause the migratetype to
> change as __isolate_free_page will attempt to change the migratetype to
> movable if it is one of the standard percpu types and we are pulling at
> least half a pageblock out. So storing the value before we isolate it
> would be problematic as well.
> 
> Undoing page isolation is the exception to the issues pointed out above,
> but in that case we are overwriting the pageblock migratetype anyway so
> the cache lines involved should all be warm from having just set the
> value.

Nothing would speak against querying the migratetype in the caller and passing it on. After all you‘re holding the zone lock, so it can‘t change.
> 


  reply	other threads:[~2019-12-17 18:46 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-05 16:22 [PATCH v15 0/7] mm / virtio: Provide support for free page reporting 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 [this message]
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
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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