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Received: from willy by casper.infradead.org with local (Exim 4.97.1 #2 (Red Hat Linux)) id 1sYPuN-0000000DZnp-1691; Mon, 29 Jul 2024 12:55:23 +0000 Date: Mon, 29 Jul 2024 13:55:23 +0100 From: Matthew Wilcox To: Chuanhua Han Cc: Barry Song <21cnbao@gmail.com>, akpm@linux-foundation.org, linux-mm@kvack.org, ying.huang@intel.com, baolin.wang@linux.alibaba.com, chrisl@kernel.org, david@redhat.com, hannes@cmpxchg.org, hughd@google.com, kaleshsingh@google.com, kasong@tencent.com, linux-kernel@vger.kernel.org, mhocko@suse.com, minchan@kernel.org, nphamcs@gmail.com, ryan.roberts@arm.com, senozhatsky@chromium.org, shakeel.butt@linux.dev, shy828301@gmail.com, surenb@google.com, v-songbaohua@oppo.com, xiang@kernel.org, yosryahmed@google.com, Chuanhua Han Subject: Re: [PATCH v5 3/4] mm: support large folios swapin as a whole for zRAM-like swapfile Message-ID: References: <20240726094618.401593-1-21cnbao@gmail.com> <20240726094618.401593-4-21cnbao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Rspam-User: X-Stat-Signature: w5m7qfj1hq7qp8qei8hgqgfajh6pm6u3 X-Rspamd-Queue-Id: 23E6A180036 X-Rspamd-Server: rspam11 X-HE-Tag: 1722257733-954355 X-HE-Meta: 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 iJY+b5pH kV5Hv00Cwp4mYBC4G42wPxv3jqllFFvxk5IsYUfNXacumlWqLa9BcpNiOSvMx3/aEpS7Di5tmi7LfPz7Ok/Dw+AY8vT1vPJ8saqbzNcY7J2OeaGCEL9m+DHBOulu+Hr+VVEVVTgxeiKigmEiNPurl6Lu37+SuXPRT3zNRyk+664ZMOirE9s+40/gVt2JDE1fiv4hOa60aBmt0kwuS/h197q01NM+hEgbpOZcas0AkhuLizGc3ovQB67ZPiRYowF0XNA2PNtg9KmJJRqSrljg/NoAgPqUk+3SN4CGX 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: On Mon, Jul 29, 2024 at 02:36:38PM +0800, Chuanhua Han wrote: > Matthew Wilcox 于2024年7月29日周一 11:51写道： > > > > On Fri, Jul 26, 2024 at 09:46:17PM +1200, Barry Song wrote: > > > - folio = vma_alloc_folio(GFP_HIGHUSER_MOVABLE, 0, > > > - vma, vmf->address, false); > > > + folio = alloc_swap_folio(vmf); > > > page = &folio->page; > > > > This is no longer correct. You need to set 'page' to the precise page > > that is being faulted rather than the first page of the folio. It was > > fine before because it always allocated a single-page folio, but now it > > must use folio_page() or folio_file_page() (whichever has the correct > > semantics for you). > > > > Also you need to fix your test suite to notice this bug. I suggest > > doing that first so that you know whether you've got the calculation > > correct. > > > > > > This is no problem now, we support large folios swapin as a whole, so > the head page is used here instead of the page that is being faulted. > You can also refer to the current code context, now support large > folios swapin as a whole, and previously only support small page > swapin is not the same. You have completely failed to understand the problem. Let's try it this way: We take a page fault at address 0x123456789000. If part of a 16KiB folio, that's page 1 of the folio at 0x123456788000. If you now map page 0 of the folio at 0x123456789000, you've given the user the wrong page! That looks like data corruption. The code in if (folio_test_large(folio) && folio_test_swapcache(folio)) { as Barry pointed out will save you -- but what if those conditions fail? What if the mmap has been mremap()ed and the folio now crosses a PMD boundary? mk_pte() will now be called on the wrong page.