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Mon, 24 Jul 2023 22:55:48 -0700 (PDT) MIME-Version: 1.0 References: <20230721094043.2506691-1-fengwei.yin@intel.com> <20230721094043.2506691-3-fengwei.yin@intel.com> In-Reply-To: <20230721094043.2506691-3-fengwei.yin@intel.com> From: Yu Zhao Date: Mon, 24 Jul 2023 23:55:12 -0600 Message-ID: Subject: Re: [RFC PATCH v2 2/4] madvise: Use notify-able API to clear and flush page table entries To: Yin Fengwei Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, minchan@kernel.org, willy@infradead.org, david@redhat.com, ryan.roberts@arm.com, shy828301@gmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 29BC140008 X-Stat-Signature: mxe49ksemjfxr1gojm7shzn4w9oqhz6m X-Rspam-User: X-HE-Tag: 1690264548-741599 X-HE-Meta: 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 FX5Glv/o y86mAnW0jLuDES0Q0xGFWTyzaItFttWmi7MKEQ5BpjPfjz9ldwtt9HPxOZfcs2mk7Je1TNNXYTnlLfRUNBAwLdyuoo0k8u1321nLjjKiqutdj5cphz5pTwnKcZ41oYQuBVkGkEm9iEQ1xkuLJ8XX1sCWAYvwRiMaN0/37WzBWD3CpP93zv+Kbms6PwSv55NWUHq2X4+eClR/wH6GRAkbXalF7fB7q7uoBmMBJwtNnQK1L2VEJIDtn0SqkzQ== 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: On Fri, Jul 21, 2023 at 3:41=E2=80=AFAM Yin Fengwei = wrote: > > Currently, in function madvise_cold_or_pageout_pte_range(), the > young bit of pte/pmd is cleared notify subscripter. > > Using notify-able API to make sure the subscripter is signaled about > the young bit clearing. > > Signed-off-by: Yin Fengwei > --- > mm/madvise.c | 18 ++---------------- > 1 file changed, 2 insertions(+), 16 deletions(-) > > diff --git a/mm/madvise.c b/mm/madvise.c > index f12933ebcc24..b236e201a738 100644 > --- a/mm/madvise.c > +++ b/mm/madvise.c > @@ -403,14 +403,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *= pmd, > return 0; > } > > - if (pmd_young(orig_pmd)) { > - pmdp_invalidate(vma, addr, pmd); > - orig_pmd =3D pmd_mkold(orig_pmd); > - > - set_pmd_at(mm, addr, pmd, orig_pmd); > - tlb_remove_pmd_tlb_entry(tlb, pmd, addr); > - } > - > + pmdp_clear_flush_young_notify(vma, addr, pmd); > folio_clear_referenced(folio); > folio_test_clear_young(folio); > if (folio_test_active(folio)) > @@ -496,14 +489,7 @@ static int madvise_cold_or_pageout_pte_range(pmd_t *= pmd, > > VM_BUG_ON_FOLIO(folio_test_large(folio), folio); > > - if (pte_young(ptent)) { > - ptent =3D ptep_get_and_clear_full(mm, addr, pte, > - tlb->fullmm); > - ptent =3D pte_mkold(ptent); > - set_pte_at(mm, addr, pte, ptent); > - tlb_remove_tlb_entry(tlb, pte, addr); > - } > - > + ptep_clear_flush_young_notify(vma, addr, pte); These two places are tricky. I agree there is a problem here, i.e., we are not consulting the mmu notifier. In fact, we do pageout on VMs on ChromeOS, and it's been a known problem to me for a while (not a high priority one). tlb_remove_tlb_entry() is batched flush, ptep_clear_flush_young() is not. But, on x86, we might see a performance improvement since ptep_clear_flush_young() doesn't flush TLB at all. On ARM, there might be regressions though. I'd go with ptep_clear_young_notify(), but IIRC, Minchan mentioned he prefers flush. So I'll let him chime in. If we do end up with ptep_clear_young_notify(), please remove mmu_gather -- it should have been done in this patch.