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[184.145.4.219]) by smtp.gmail.com with ESMTPSA id q7sm5509867qki.17.2021.05.21.11.57.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 21 May 2021 11:57:56 -0700 (PDT) Date: Fri, 21 May 2021 14:57:54 -0400 From: Peter Xu To: Peter Collingbourne Cc: Andrew Morton , Kostya Kortchinsky , Evgenii Stepanov , linux-mm@kvack.org, Andrea Arcangeli Subject: Re: [PATCH v3] mm: improve mprotect(R|W) efficiency on pages referenced once Message-ID: References: <20210429214801.2583336-1-pcc@google.com> MIME-Version: 1.0 In-Reply-To: <20210429214801.2583336-1-pcc@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=IeG+t6yA; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf13.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 216.205.24.124) smtp.mailfrom=peterx@redhat.com X-Stat-Signature: deg1bpurtt64a7ouu53z11ecy55ny88b X-Rspamd-Queue-Id: 07CDAE000804 X-Rspamd-Server: rspam02 X-HE-Tag: 1621623478-33070 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 Thu, Apr 29, 2021 at 02:48:01PM -0700, Peter Collingbourne wrote: > @@ -132,9 +134,12 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, > } > > /* Avoid taking write faults for known dirty pages */ > - if (dirty_accountable && pte_dirty(ptent) && > - (pte_soft_dirty(ptent) || > - !(vma->vm_flags & VM_SOFTDIRTY))) { > + if ((dirty_accountable || > + (anon_writable && > + page_mapcount(pte_page(ptent)) == 1)) && > + pte_dirty(ptent) && > + (pte_soft_dirty(ptent) || > + !(vma->vm_flags & VM_SOFTDIRTY))) { > ptent = pte_mkwrite(ptent); > } > ptep_modify_prot_commit(vma, addr, pte, oldpte, ptent); This breaks uffd-wp anonymous page. I think we'd at least need below to be squashed: diff --git a/mm/mprotect.c b/mm/mprotect.c index ed10a790933e..6cb531eab811 100644 --- a/mm/mprotect.c +++ b/mm/mprotect.c @@ -139,6 +139,7 @@ static unsigned long change_pte_range(struct vm_area_struct *vma, pmd_t *pmd, (anon_writable && page_mapcount(pte_page(ptent)) == 1)) && pte_dirty(ptent) && + !pte_uffd_wp(ptent) && (pte_soft_dirty(ptent) || !(vma->vm_flags & VM_SOFTDIRTY))) { ptent = pte_mkwrite(ptent); It'll be good to start thinking about how to not continue growing this if clause condition, though.. -- Peter Xu