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Tue, 01 Aug 2023 13:29:09 -0700 (PDT) MIME-Version: 1.0 References: <20230731171233.1098105-1-surenb@google.com> <20230731171233.1098105-2-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 1 Aug 2023 13:28:56 -0700 Message-ID: Subject: Re: [PATCH 1/6] mm: enable page walking API to lock vmas during the walk To: Linus Torvalds Cc: akpm@linux-foundation.org, jannh@google.com, willy@infradead.org, liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com, ldufour@linux.ibm.com, vbabka@suse.cz, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, hannes@cmpxchg.org, dave@stgolabs.net, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 81E9B40004 X-Rspam-User: X-Stat-Signature: 5esseo3ws7ghyz1zuuax4bdo9qt1oh5h X-Rspamd-Server: rspam01 X-HE-Tag: 1690921750-899547 X-HE-Meta: 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 j0O3kWzB yBA+cp2H7QK0+bjonmikUzO92EIXH/XnW0yCmnRQX+UF0unG9YGYcb1LPma8xEQFwFnGe0BAssXcafumBkHyURlrNBjYssjnLO+qS1PIinke97bpjseHjrADQzqyCBkBrlDGzXZQpRKwnXe7udRna5k/LFCoReXk6QdoQCh0ORqZ2glXJK4YIauRDBcsZ1LTf1VUmgal9heLfBr1zoJvGnX+VWNbVNpDXxqF8W3fND2IdGIn4A5SqnMnPxEN/4a0RF99ZOc4Qhp3AUZbwU4HQQm90zYlJfy40c87PKkne8Lc9KgGIlAzGAYXwYA== 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 Mon, Jul 31, 2023 at 1:24=E2=80=AFPM Suren Baghdasaryan wrote: > > On Mon, Jul 31, 2023 at 12:33=E2=80=AFPM Linus Torvalds > wrote: > > > > On Mon, 31 Jul 2023 at 12:31, Suren Baghdasaryan wr= ote: > > > > > > I got the idea but a couple of modifications, if I may. > > > > Ack, sounds sane to me. > > Ok, I'll wait for more feedback today and will post an update tomorrow. T= hanks! I have the new patchset ready but I see 3 places where we walk the pages after mmap_write_lock() while *I think* we can tolerate concurrent page faults (don't need to lock the vmas): s390_enable_sie() break_ksm() clear_refs_write() In all these walks we lock PTL when modifying the page table entries, that's why I think we can skip locking the vma but maybe I'm missing something? Could someone please check these 3 cases and confirm or deny my claim? Thanks, Suren. > > > > > Linus