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[2003:cb:c719:5b00:61af:900f:3aef:3af3]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4247d0c54besm14060185e9.25.2024.06.19.23.52.57 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 19 Jun 2024 23:52:58 -0700 (PDT) Message-ID: <2a358ff4-4219-4262-9225-d9aab14445f6@redhat.com> Date: Thu, 20 Jun 2024 08:52:57 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 0/9] support large folio swap-out and swap-in for shmem To: Hugh Dickins , Andrew Morton , Barry Song Cc: Baolin Wang , willy@infradead.org, wangkefeng.wang@huawei.com, chrisl@kernel.org, ying.huang@intel.com, 21cnbao@gmail.com, ryan.roberts@arm.com, shy828301@gmail.com, ziy@nvidia.com, ioworker0@gmail.com, da.gomez@samsung.com, p.raghav@samsung.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20240618130538.ffab3ce1b4e66e3ba095d8cf@linux-foundation.org> <475f0f2c-afc7-4225-809f-93c93f45c830@linux.alibaba.com> <2683b71d-aebd-5527-348c-18c0e021b653@google.com> <25ae21b4-23d5-73ba-2e0a-e642ec4b69a0@google.com> From: David Hildenbrand Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Stat-Signature: oqgp5rrrix4q4hf5ijz3gyk5wu1pww11 X-Rspamd-Queue-Id: 49998180003 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1718866383-705723 X-HE-Meta: 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 O6D2+6ZB 5Oyqv3tk/wXVj3S2XESE0aW/xQrlNkamoFClUvHl2KWpfj1OTqkc8H2YLfnYmQZV1+hXc2Bl/Tn+PYH1LZYBfFN8AU+Pb0Dh+Mmou7xP8XX/75gUUFQfFwhGGZmMmzTEL172Ca+d7NaaeXxryjJCj6GVp1lfr+vavUoB+5+Ha0qmMdR8l+w4FYVqnh817T2Yb4nDh+m2C1BG7UbX8KNq86QoJMXo19c7aXB/KR92GqFgIxoq+Z2DtLTLjV8Cka3hdalRZYX+QXSWbNBLOw6cNDCZoQvbvpUWUDvbkOZwgCmOis5bhe6SwgnV09EN5OSAgmPbZX1mqZsiacw/7PC3WGn5Qy420uiwMYm+uiGwSLWvQQuX0prAoxVu2pg== 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: List-Subscribe: List-Unsubscribe: > > (I do have doubts about Barry's: the "_new" in folio_add_new_anon_rmap() > was all about optimizing a known-exclusive case, so it surprises me > to see it being extended to non-exclusive; and I worry over how its > atomic_set(&page->_mapcount, 0)s can be safe when non-exclusive (but > I've never caught up with David's exclusive changes, I'm out of date). We discussed that a while ago: if we wouldn't be holding the folio lock in the "folio == swapcache" at that point (which we do for both do_swap_page() and unuse_pte()) things would already be pretty broken. That's I added a while ago: if (unlikely(!folio_test_anon(folio))) { VM_WARN_ON_FOLIO(!folio_test_locked(folio), folio); /* * For a PTE-mapped large folio, we only know that the single * PTE is exclusive. Further, __folio_set_anon() might not get * folio->index right when not given the address of the head * page. */ ... We should probably move that VM_WARN_ON_FOLIO() to folio_add_new_anon_rmap() and document that it's required in the non-exclusive case. > > But even if those are wrong, I'd expect them to tend towards a mapped > page becoming unreclaimable, then "Bad page map" when munmapped, > not to any of the double-free symptoms I've actually seen.) What's the first known-good commit? -- Cheers, David / dhildenb