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charset="UTF-8" X-Stat-Signature: pd6ramhne9iebobknqh4crg86mm953uw X-Rspam-User: X-Rspamd-Queue-Id: B2FF2100009 X-Rspamd-Server: rspam06 X-HE-Tag: 1674077592-344658 X-HE-Meta: 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 Ku4NVCkI LRGFE/JiCikYPxBf+lmiq5EPqtqSWZD8v8dk9jiuymSMK577kSCiGclEDMg== 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 Tue, Jan 17, 2023 at 6:44 PM Matthew Wilcox wrote: > > On Tue, Jan 17, 2023 at 05:06:57PM -0800, Suren Baghdasaryan wrote: > > On Tue, Jan 17, 2023 at 7:47 AM Michal Hocko wrote: > > > > > > On Mon 09-01-23 12:53:23, Suren Baghdasaryan wrote: > > > > Introduce lock_vma_under_rcu function to lookup and lock a VMA during > > > > page fault handling. When VMA is not found, can't be locked or changes > > > > after being locked, the function returns NULL. The lookup is performed > > > > under RCU protection to prevent the found VMA from being destroyed before > > > > the VMA lock is acquired. VMA lock statistics are updated according to > > > > the results. > > > > For now only anonymous VMAs can be searched this way. In other cases the > > > > function returns NULL. > > > > > > Could you describe why only anonymous vmas are handled at this stage and > > > what (roughly) has to be done to support other vmas? lock_vma_under_rcu > > > doesn't seem to have any anonymous vma specific requirements AFAICS. > > > > TBH I haven't spent too much time looking into file-backed page faults > > yet but a couple of tasks I can think of are: > > - Ensure that all vma->vm_ops->fault() handlers do not rely on > > mmap_lock being read-locked; > > I think this way lies madness. There are just too many device drivers > that implement ->fault. My plan is to call the ->map_pages() method > under RCU without even read-locking the VMA. If that doesn't satisfy > the fault, then drop all the way back to taking the mmap_sem for read > before calling into ->fault. Sounds reasonable to me but I guess the devil is in the details... >