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Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [PATCH -v4 8/9] migrate_pages: batch flushing TLB To: Huang Ying , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Zi Yan , Yang Shi , Baolin Wang , Oscar Salvador , Matthew Wilcox , Bharata B Rao , Alistair Popple , Minchan Kim , Mike Kravetz , Hyeonggon Yoo <42.hyeyoo@gmail.com> References: <20230206063313.635011-1-ying.huang@intel.com> <20230206063313.635011-9-ying.huang@intel.com> From: haoxin In-Reply-To: <20230206063313.635011-9-ying.huang@intel.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 2404B40010 X-Stat-Signature: ebnz4uy7zwzsij9xo96145c1fxsbny9n X-HE-Tag: 1675791850-67676 X-HE-Meta: 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 SY9DShIQ MmowcP0mY4lKFEtm5ipoQLc0f5/Bi9KM7cKCMInnuCpmKpzEB2XVrq9DElBhr+GZcK2jJiWmpGxXsxE5OqW2dEV9E4MljbmolThGK9XtdWKun9V7tM+rqffKnfeg1Is67G1JbZa+72zt0C2xhpwu31PJVFo/3ucrGWXUGYbwBQOekxdNkMm5xzCyhAZ/K5VUFDQSI8U0jGryWqek+ZXpeXvJOlLXEdV4jwZA5vrXfUIsfbBNhkpCX4KCW2z8+YvImokAv16YGCdeC9p7/gcpVqfr2rb3qXKgCCagKqBgfOmmZsJATq1ELtw59McAvEMJ0SXMmlcgYKhrkEV79P2MPpoqaNfvOmllMZTvhDn6ZZ+vglnlq3J4wfxTEgnCQy1yL5i2A3SMSoJ2lkJdEdDzzVG/1VZgqYNV/qxv8eW9QOx+e2/xezVn0tiRLK5++73ez1urYj+uzoI6wZDQPKrMOjYdOFN2X6Au9FrJMMdoggnJhKYP5QaH/yyD1ZTG/dUfIqQdLFNzWzhUQNdIBUZ/Bv/7u39UL+On/aMF0vLiruUS2prA0qqvOpSY2hANKUSCF60GI 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: 在 2023/2/6 下午2:33, Huang Ying 写道: > 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: > + 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); Nice work， Reviewed-by: Xin Hao > + > + 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) &&