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Howlett" , Suren Baghdasaryan , akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, peterz@infradead.org, ldufour@linux.ibm.com, paulmck@kernel.org, mingo@redhat.com, will@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, chriscli@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, rppt@kernel.org, jannh@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, leewalsh@google.com, posk@google.com, michalechner92@googlemail.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 76C1620014 X-Stat-Signature: fa4d7an5icpoz9u73wjpch1stdbz7kzw X-Rspam-User: X-HE-Tag: 1677255576-833114 X-HE-Meta: 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 OFcUlnq0 DpgIcgyaTtTf8JhED36Xhqk3P+DTS/vboWjvMo8if4UZTOymnY9T8ivWq/QGwdcVBM51UcymBWhprxaffN6bx1qew3oahCVdAUto/qKsuCxzKwIvOur7P9JBEexpL/tjnvrS7yevmqRKjXs0eo73VqM0KEe6sI0sp0Z9JDQA5y+MJIimcqTbJGIT0qsNuazZEilUHNmAMn4T1KdimAH9daf1Lz18bAV8Hx38ps6NexNg6UHaWRDCVDhzITi8HSWxzpRig6yooMYkt77uPAcBD8UemJ8cgYJpaP0sFo2GzkCodvD1AxgzAzhPInqD98SnoHGzVRPhCk1MhtkB9N4dhM89yT7/c15hq0QKuL792EaetZUL5JF2OCUqHQBFYVzfio/WORfQ/7i4H8/FJ7rSYux8ygxLG++VVJRwQmoA97gpcnQM= 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 Fri, Feb 24, 2023 at 8:14 AM Liam R. Howlett wrote: > > * Suren Baghdasaryan [230223 21:06]: > > On Thu, Feb 23, 2023 at 5:46 PM Liam R. Howlett wrote: > > > > > > * Suren Baghdasaryan [230223 16:16]: > > > > On Thu, Feb 23, 2023 at 12:28 PM Liam R. Howlett > > > > wrote: > > > > > > > > > > > > > > > Wait, I figured a better place to do this. > > > > > > > > > > init_multi_vma_prep() should vma_start_write() on any VMA that is passed > > > > > in.. that we we catch any modifications here & in vma_merge(), which I > > > > > think is missed in this patch set? > > > > > > > > Hmm. That looks like a good idea but in that case, why not do the > > > > locking inside vma_prepare() itself? From the description of that > > > > function it sounds like it was designed to acquire locks before VMA > > > > modifications, so would be the ideal location for doing that. WDYT? > > > > > > That might be even better. I think it will result in even less code. > > > > Yes. > > > > > > > > There is also a vma_complete() which might work to call > > > vma_end_write_all() as well? > > > > If there are other VMAs already locked before vma_prepare() then we > > would unlock them too. Safer to just let mmap_unlock do > > vma_end_write_all(). > > > > > > > > > The only concern is vma_adjust_trans_huge() being called before > > > > vma_prepare() but I *think* that's safe because > > > > vma_adjust_trans_huge() does its modifications after acquiring PTL > > > > lock, which page fault handlers also have to take. Does that sound > > > > right? > > > > > > I am not sure. We are certainly safe the way it is, and the PTL has to > > > be safe for concurrent faults.. but this could alter the walk to a page > > > table while that walk is occurring and I don't think that happens today. > > > > > > It might be best to leave the locking order the way you have it, unless > > > someone can tell us it's safe? > > > > Yes, I have the same feelings about changing this. > > > > > > > > We could pass through the three extra variables that are needed to move > > > the vma_adjust_trans_huge() call within that function as well? This > > > would have the added benefit of having all locking grouped in the one > > > location, but the argument list would be getting long, however we could > > > use the struct. > > > > Any issues if I change the order to have vma_prepare() called always > > before vma_adjust_trans_huge()? That way the VMA will always be locked > > before vma_adjust_trans_huge() executes and we don't need any > > additional arguments. > > I preserved the locking order from __vma_adjust() to ensure there was no > issues. > > I am not sure but, looking through the page table information [1], it > seems that vma_adjust_trans_huge() uses the pmd lock, which is part of > the split page table lock. According to the comment in rmap, it should > be fine to reverse the ordering here. > > Instead of: > > mmap_lock() > vma_adjust_trans_huge() > pte_lock > pte_unlock > > vma_prepare() > mapping->i_mmap_rwsem lock > anon_vma->rwsem lock > > > > vma_complete() > anon_vma->rwsem unlock > mapping->i_mmap_rwsem unlock > > mmap_unlock() > > --------- > > We would have: > > mmap_lock() > vma_prepare() > mapping->i_mmap_rwsem lock > anon_vma->rwsem lock > > vma_adjust_trans_huge() > pte_lock > pte_unlock > > > > vma_complete() > anon_vma->rwsem unlock > mapping->i_mmap_rwsem unlock > > mmap_unlock() > > > Essentially, increasing the nesting of the pte lock, but not violating > the ordering. > > 1. https://docs.kernel.org/mm/split_page_table_lock.html Thanks for the confirmation, Liam. I'll make the changes and test over the weekend. If everything's still fine, I will post the next version with these and other requested changes on Monday. > > > > > > > > > remove & remove2 should be be detached in vma_prepare() or > > > vma_complete() as well? > > > > They are marked detached in vma_complete() (see > > https://lore.kernel.org/all/20230216051750.3125598-25-surenb@google.com/) > > and that should be enough. We should be safe as long as we mark them > > detached before unlocking the VMA. > > > > Right, Thanks. > > ... > > -- > To unsubscribe from this group and stop receiving emails from it, send an email to kernel-team+unsubscribe@android.com. >