From: Peter Xu <peterx@redhat.com>
To: Peter Collingbourne <pcc@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Kostya Kortchinsky <kostyak@google.com>,
Evgenii Stepanov <eugenis@google.com>,
linux-mm@kvack.org, Andrea Arcangeli <aarcange@redhat.com>
Subject: Re: [PATCH v3] mm: improve mprotect(R|W) efficiency on pages referenced once
Date: Fri, 21 May 2021 14:57:54 -0400 [thread overview]
Message-ID: <YKgCsmMVp3wNLLBB@t490s> (raw)
In-Reply-To: <20210429214801.2583336-1-pcc@google.com>
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
prev parent reply other threads:[~2021-05-21 18:58 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 21:48 Peter Collingbourne
2021-05-21 18:57 ` Peter Xu [this message]
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