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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-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 6FFB0100008 X-Stat-Signature: qds8mzyp933upowjjo1oeaxepbc4zynh X-HE-Tag: 1677519241-372354 X-HE-Meta: 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 hZyRgAGX C1tKGr6jjAZ0G/Nr5dXZa0JeAOCHtaIrHP5u9HXAKEtQ9ZHwWVJ/0oE2DnF5IoBMDs39177JjvIMffNUJtLv4TvEFzWeSAoYY/e5SWdS4x5PzasLxSlNCEb9hj+VuSr0YHMBEveZMJw75slOxWtYwEUmQ2oQDrhyJpiNx30HjteFqko2p/CW0tWW/rvcLCFnI3o9nQ96zvoIFzYKRDk/yVxSMVM3BlHQEoBbFqx92GoXFb/uVOCRJvW2NZbxYcOkkMGDUrhuF/uE/mOuCHw9ZA8qklRX2ukNg/j2TMftKGQGycujA8Cr+HULgb0T11rWuuvZMyFFmhzV+U3p4GlziMH3XTNluu6U8g4yKs5Xwx+tA2GXVdTWY3gaGZL9WtJY6fZG8YLjTW/8RBE2Yx6sDUzRrqLeldz/S/o2lsm7gNJHFrpo= 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 8:19 AM Suren Baghdasaryan wrote: > > 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. Weekend testing results look good with all the changes. I'll post v4 shortly. Thanks, Suren. > > > > > > > > > > > > > > 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. > >