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X-IronPort-AV: E=McAfee;i="6500,9779,10614"; a="327468233" X-IronPort-AV: E=Sophos;i="5.97,280,1669104000"; d="scan'208";a="327468233" Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga102.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Feb 2023 03:28:45 -0800 X-IronPort-AV: E=McAfee;i="6500,9779,10614"; a="791167966" X-IronPort-AV: E=Sophos;i="5.97,280,1669104000"; d="scan'208";a="791167966" Received: from yhuang6-desk2.sh.intel.com (HELO yhuang6-desk2.ccr.corp.intel.com) ([10.238.208.55]) by orsmga004-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 Feb 2023 03:28:42 -0800 From: "Huang, Ying" To: Zi Yan Cc: Andrew Morton , , , Yang Shi , Baolin Wang , Oscar Salvador , "Matthew Wilcox" , Bharata B Rao , "Alistair Popple" , haoxin , Minchan Kim , Mike Kravetz , Hyeonggon Yoo <42.hyeyoo@gmail.com> Subject: Re: [PATCH -v4 8/9] migrate_pages: batch flushing TLB References: <20230206063313.635011-1-ying.huang@intel.com> <20230206063313.635011-9-ying.huang@intel.com> Date: Wed, 08 Feb 2023 19:27:53 +0800 In-Reply-To: (Zi Yan's message of "Tue, 07 Feb 2023 09:52:28 -0500") Message-ID: <878rh8gzwm.fsf@yhuang6-desk2.ccr.corp.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=ascii X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: ozzp5rj1catk4wi4g5yjp155irarq5m6 X-Rspamd-Queue-Id: 35E7E40007 X-HE-Tag: 1675855737-442208 X-HE-Meta: U2FsdGVkX18Ycwgalv/FjqNh9sZ3wvvSBAknFwo7peG/XUJrPxsH/3n1ogBVmgWUxsYCcyVcuJGm5JK2uHTCI+mZ2zDjtfR0JL6LXARh+Q8a+FxBqyMucETe0XcligcB6VxXqeJXngvynUfYvLRnHM+5d0eoppZ0Jt9JNx1SwwJFQNhLQDvYVucJzJYIFfFlZUVVNHD90arMWbh71b8KcAJu1W5mU86QqttyQ1C1fIUU61CLVkmvOOlGEsypzzPTuJ+NtsZnKyxu14WKn1e2P9AhHrKJ9YK8BzXxxj+fy4IYwSm7d9mAPlF5hMNxj8/iDW+TdWgcO9JAPDc8ORW2f/ac9Js7PxcrGDi2qEKVSGc3qEYAHqbxbdRnOo6g1xBsRHgHzIFubqZcdt6WacwpXR2LqFDTVSCyzAGOew4NkWHV4UqvaFZ36oIhOaEfHzLW3u7mFynhXfJ8qtK8MGxR0iJ3FBXU7jPrhtx0mmqTBC3DyyTptyIMxBFBHA9XYwjHPYIjjUWrAAD8d1VBo04Kx0Eb1nui427z56yEQxie2IIkH5TAXShGam8NKvoIVLy5MZV7zUKKu+V0mKUekYfhUkBtWT8DQlFFta2t/XK8nwaZGhDpCKv6fIjns/HAqfpu7wOKsj/Qx2VoUo7DRm1+oSCiXLBrjdm6hXIPzXiiJCMBrVjJ7CJ/k4a4Oidw22Gvj/e5n5hg1/QtTFs7ddYB5LZVbBLWJcqflYSBjlGtM2888wis+PNXxLxY9Dj0oEnv2poi4n7BPQnQZ8VXwnth2s1zDDBXCGeTAi872EhdU+dbatg5wPgn3khXRQl3BZEDc0ZSAfFrEsuwvoWydhUarK/hmI2+ePRou8swtm1UVrQVeklDPC0HmXOR5EhR/FJGeMd+cdJNgFMR/XPLVnLNqyAcCeKd1xykK259euGjllBMQx8GteS6VU2rMfmUxvakFO9qkv7+6M2GuUefKuz JYzli2Rl 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: Zi Yan writes: > On 6 Feb 2023, at 1:33, Huang Ying wrote: > >> The TLB flushing will cost quite some CPU cycles during the folio >> migration in some situations. For example, when migrate a folio of a >> process with multiple active threads that run on multiple CPUs. After >> batching the _unmap and _move in migrate_pages(), the TLB flushing can >> be batched easily with the existing TLB flush batching mechanism. >> This patch implements that. >> >> We use the following test case to test the patch. >> >> 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%. >> >> NOTE: TLB flushing is batched only for normal folios, not for THP >> folios. Because the overhead of TLB flushing for THP folios is much >> lower than that for normal folios (about 1/512 on x86 platform). >> >> Signed-off-by: "Huang, Ying" >> Cc: Zi Yan >> Cc: Yang Shi >> Cc: Baolin Wang >> Cc: Oscar Salvador >> Cc: Matthew Wilcox >> Cc: Bharata B Rao >> Cc: Alistair Popple >> Cc: haoxin >> Cc: Minchan Kim >> Cc: Mike Kravetz >> Cc: Hyeonggon Yoo <42.hyeyoo@gmail.com> >> --- >> mm/migrate.c | 4 +++- >> mm/rmap.c | 20 +++++++++++++++++--- >> 2 files changed, 20 insertions(+), 4 deletions(-) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index 9378fa2ad4a5..ca6e2ff02a09 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1230,7 +1230,7 @@ static int migrate_folio_unmap(new_page_t get_new_page, free_page_t put_new_page >> /* Establish migration ptes */ >> VM_BUG_ON_FOLIO(folio_test_anon(src) && >> !folio_test_ksm(src) && !anon_vma, src); >> - try_to_migrate(src, 0); >> + try_to_migrate(src, TTU_BATCH_FLUSH); >> page_was_mapped = 1; >> } >> >> @@ -1781,6 +1781,8 @@ static int migrate_pages_batch(struct list_head *from, new_page_t get_new_page, >> stats->nr_thp_failed += thp_retry; >> stats->nr_failed_pages += nr_retry_pages; >> move: > > Maybe a comment: > /* Flush TLBs for all the unmapped pages */ OK. Will do that in the next version. Best Regards, Huang, Ying >> + try_to_unmap_flush(); >> + >> retry = 1; >> for (pass = 0; >> pass < NR_MAX_MIGRATE_PAGES_RETRY && (retry || large_retry); >> diff --git a/mm/rmap.c b/mm/rmap.c >> index b616870a09be..2e125f3e462e 100644 >> --- a/mm/rmap.c >> +++ b/mm/rmap.c >> @@ -1976,7 +1976,21 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, >> } else { >> flush_cache_page(vma, address, pte_pfn(*pvmw.pte)); >> /* Nuke the page table entry. */ >> - pteval = ptep_clear_flush(vma, address, pvmw.pte); >> + if (should_defer_flush(mm, flags)) { >> + /* >> + * We clear the PTE but do not flush so potentially >> + * a remote CPU could still be writing to the folio. >> + * If the entry was previously clean then the >> + * architecture must guarantee that a clear->dirty >> + * transition on a cached TLB entry is written through >> + * and traps if the PTE is unmapped. >> + */ >> + pteval = ptep_get_and_clear(mm, address, pvmw.pte); >> + >> + set_tlb_ubc_flush_pending(mm, pte_dirty(pteval)); >> + } else { >> + pteval = ptep_clear_flush(vma, address, pvmw.pte); >> + } >> } >> >> /* Set the dirty flag on the folio now the pte is gone. */ >> @@ -2148,10 +2162,10 @@ void try_to_migrate(struct folio *folio, enum ttu_flags flags) >> >> /* >> * Migration always ignores mlock and only supports TTU_RMAP_LOCKED and >> - * TTU_SPLIT_HUGE_PMD and TTU_SYNC flags. >> + * TTU_SPLIT_HUGE_PMD, TTU_SYNC, and TTU_BATCH_FLUSH flags. >> */ >> if (WARN_ON_ONCE(flags & ~(TTU_RMAP_LOCKED | TTU_SPLIT_HUGE_PMD | >> - TTU_SYNC))) >> + TTU_SYNC | TTU_BATCH_FLUSH))) >> return; >> >> if (folio_is_zone_device(folio) && >> -- >> 2.35.1 > > Everything else looks good to me. Reviewed-by: Zi Yan > > -- > Best Regards, > Yan, Zi