Messages in this thread | | | Date | Thu, 22 Sep 2022 11:47:41 +0800 | Subject | Re: [RFC 0/6] migrate_pages(): batch TLB flushing | From | haoxin <> |
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Hi Huang,
This is an exciting change, but on ARM64 machine the TLB flushing are not through IPI, it depends on 'vale1is'
instruction,so I'm wondering if there's also a benefit on arm64, and I'm going to test it on an ARM64 machine.
在 2022/9/21 下午11:47, Zi Yan 写道: > On 21 Sep 2022, at 2:06, Huang Ying wrote: > >> From: "Huang, Ying" <ying.huang@intel.com> >> >> Now, migrate_pages() migrate pages one by one, like the fake code as >> follows, >> >> for each page >> unmap >> flush TLB >> copy >> restore map >> >> If multiple pages are passed to migrate_pages(), there are >> opportunities to batch the TLB flushing and copying. That is, we can >> change the code to something as follows, >> >> for each page >> unmap >> for each page >> flush TLB >> for each page >> copy >> for each page >> restore map >> >> The total number of TLB flushing IPI can be reduced considerably. And >> we may use some hardware accelerator such as DSA to accelerate the >> page copying. >> >> So in this patch, we refactor the migrate_pages() implementation and >> implement the TLB flushing batching. Base on this, hardware >> accelerated page copying can be implemented. >> >> If too many pages are passed to migrate_pages(), in the naive batched >> implementation, we may unmap too many pages at the same time. The >> possibility for a task to wait for the migrated pages to be mapped >> again increases. So the latency may be hurt. To deal with this >> issue, the max number of pages be unmapped in batch is restricted to >> no more than HPAGE_PMD_NR. That is, the influence is at the same >> level of THP migration. >> >> We use the following test to measure the performance impact of the >> patchset, >> >> On a 2-socket Intel server, >> >> - Run pmbench memory accessing benchmark >> >> - Run `migratepages` to migrate pages of pmbench between node 0 and >> node 1 back and forth. >> >> With the patch, the TLB flushing IPI reduces 99.1% during the test and >> the number of pages migrated successfully per second increases 291.7%. > Thank you for the patchset. Batching page migration will definitely > improve its throughput from my past experiments[1] and starting with > TLB flushing is a good first step. > > BTW, what is the rationality behind the increased page migration > success rate per second? > >> This patchset is based on v6.0-rc5 and the following patchset, >> >> [PATCH -V3 0/8] migrate_pages(): fix several bugs in error path >> https://lore.kernel.org/lkml/20220817081408.513338-1-ying.huang@intel.com/ >> >> The migrate_pages() related code is converting to folio now. So this >> patchset cannot apply recent akpm/mm-unstable branch. This patchset >> is used to check the basic idea. If it is OK, I will rebase the >> patchset on top of folio changes. >> >> Best Regards, >> Huang, Ying > > [1] https://lwn.net/Articles/784925/ > > -- > Best Regards, > Yan, Zi
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