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Mon, 28 Aug 2023 12:38:18 -0700 (PDT) Date: Mon, 28 Aug 2023 20:38:17 +0100 From: Lorenzo Stoakes To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, Shuah Khan , Vlastimil Babka , Michal Hocko , Linus Torvalds , Kirill A Shutemov , "Liam R. Howlett" , "Paul E. McKenney" , Suren Baghdasaryan , Kalesh Singh , Lokesh Gidra Subject: Re: [PATCH v5 6/7] selftests: mm: Add a test for remapping within a range Message-ID: References: <20230822015501.791637-1-joel@joelfernandes.org> <20230822015501.791637-7-joel@joelfernandes.org> <08ce8c61-e7a2-417a-a3cc-d20861753ae8@lucifer.local> <20230828185912.GD1621761@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230828185912.GD1621761@google.com> X-Rspamd-Queue-Id: BB4AE20009 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: k6akmirrgsc9uh7d9gu4x9kawnam76np X-HE-Tag: 1693251500-246162 X-HE-Meta: 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 eqybzEpd jfbuGYyNcE1T82CAe7P+EXd3E50i3xad4O+5z4LZhabUXsf8O6NosmPSrpGFV07J6BlrCPYWb6k+VegjeZRZm8Vovk7dm+eNxijQ9QJ0AqOunSgm7445YgogMKNHaHrSf4/fuSotcmRQ9gRpmGux83CojCRU4bhR/4yOuTV16FxkV0Czs1s3TemCcsE1SmmDfUvjmCCUOww5XmDlUngZjHV+8zSsPn2iSPZj/FtIRZJoLOx3tfeCCBRSr/cF0mUd5TJhYLxvvwh8XbaizcLQxPrYhhaJsErhFBwvQfy/jdONMpXuEA8LzYYMcXoCUaQPP/Sh2ckTM0vO+w1ZSNLjh170ekLtwkIRYixHoEeorrL9FuO8X85utByycoXMX8XG5orGzT9NvmIiqIdLndnvkxlpKWQpN8Bdj1pPy5MYiwi5DOkFocV+CkAWHco2Mgd5TfEaorpZRu7v3THLaE20OkW09NA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000014, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Aug 28, 2023 at 06:59:12PM +0000, Joel Fernandes wrote: > On Sun, Aug 27, 2023 at 11:15:20AM +0100, Lorenzo Stoakes wrote: > > On Sun, Aug 27, 2023 at 10:57:59AM +0100, Lorenzo Stoakes wrote: > > [snip] > > > > > > +/* > > > > + * Verify that an mremap within a range does not cause corruption > > > > + * of unrelated part of range. > > > > + * > > > > + * Consider the following range which is 2MB aligned and is > > > > + * a part of a larger 10MB range which is not shown. Each > > > > + * character is 256KB below making the source and destination > > > > Just noticed, I think you misspeak here, as this test doens't seem to > > offset by 256 KiB? That is the strategy for mremap_move_1mb_from_start() > > rather than this test so perhaps comment needs to be moved around? > > > > * 2MB each. The lower case letters are moved (s to d) and the > > * upper case letters are not moved. The below test verifies > > * that the upper case S letters are not corrupted by the > > * adjacent mremap. > > * > > * |DDDDddddSSSSssss| > > */ > > static void mremap_move_within_range(char pattern_seed) > > Here we are moving 1MB within a 4MB zone of a large mapping. Each character > 's' or 'd' is 256KB. The 256KB there is just for illustration and not really > significant as such. The 'ssss' is moved to 'dddd' 1MB each. Here we make Ahhh I see. I find that a little confusing here, perhaps clearer to say 'each block of letters is 1 MiB in size' or something? > sure that this move did not accidentally corrupt 'SSSS' and 'DDDD' due to > alignment optimization. Basically to protect from this, we check in the code > that the source address is beginning of the VMA: > + if (vma->vm_start != addr_to_align) > + return false; > > But you did point an issue which is I need to change the comment from 'larger > 10MB' to 'larger 20MB'. Did I? Well happy to take credit ;) > > In the mremap_move_1mb_from_start() test, I request for an alignment of > 1.25MB so that when I align down, I fall no mapping. This is to catch a bug > that Linus found which is that just because an aligned down address did not > fall on a mapping, that doesn't mean we can just move it at PMD-level > otherwise we destroy the mapping. Yeah that case it all makes sense in, just wondered if the comment belonged there but just me not reading your comment carefully! > > I do need to update the test name in mremap_move_1mb_from_start() to: "mremap > move 1mb from start at 1MB+256KB aligned src". So thanks for point this! > > Would that sort it out or is there still something in the comment I am > missing? Just the suggestion above re: clarification, however it's not a show stopper more of a small nit. > > Thanks! > > - Joel Cheers! > > > > > > > > > > [snip]