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. >
next prev parent 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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