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Fri, 09 Jun 2023 11:49:25 -0700 (PDT) MIME-Version: 1.0 References: <20230609005158.2421285-1-surenb@google.com> <20230609005158.2421285-6-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Fri, 9 Jun 2023 11:49:14 -0700 Message-ID: Subject: Re: [PATCH v2 5/6] mm: implement folio wait under VMA lock To: Matthew Wilcox Cc: akpm@linux-foundation.org, hannes@cmpxchg.org, mhocko@suse.com, josef@toxicpanda.com, jack@suse.cz, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, michel@lespinasse.org, liam.howlett@oracle.com, jglisse@google.com, vbabka@suse.cz, minchan@google.com, dave@stgolabs.net, punit.agrawal@bytedance.com, lstoakes@gmail.com, hdanton@sina.com, apopple@nvidia.com, peterx@redhat.com, ying.huang@intel.com, david@redhat.com, yuzhao@google.com, dhowells@redhat.com, hughd@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, pasha.tatashin@soleen.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: e1ztmic8zg5rkffhdrheuhyjouwecgnd X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: E02A14001A X-HE-Tag: 1686336566-542381 X-HE-Meta: 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 DSTJOFOn jUIJcNG87G332UDvyZ8ZrDJw9tHwJPJ/AYxIe5B8Bl17tc3tJbu2sMPcJLW3oC49LNQx4MossuYb3GJUSX16gvTOkNjbffR8M9C9Wvfxoaem7+JPjsmTxdhs7Ox0LqvuaiuRG5pN2PEtSO2SlchiNKpKjCVosjCYyt3WVIXXK5dgD0yaD1pa8L05RaUfToDbLef65MUGIfkWcHbQy7jDcaMZpHMaS+VBzF3/tVaVMcgIxrHU2EexeqtaHnxa/zWbeMoavmQ40zoHWi3rVea0WfrXKphkiRbTQqT2s 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, Jun 9, 2023 at 8:03=E2=80=AFAM Matthew Wilcox = wrote: > > On Thu, Jun 08, 2023 at 05:51:57PM -0700, Suren Baghdasaryan wrote: > > static inline bool folio_lock_or_retry(struct folio *folio, > > - struct mm_struct *mm, unsigned int flags) > > + struct vm_area_struct *vma, unsigned int flags, > > + bool *lock_dropped) > > I hate these double-return-value functions. > > How about this for an API: > > vm_fault_t folio_lock_fault(struct folio *folio, struct vm_fault *vmf) > { > might_sleep(); > if (folio_trylock(folio)) > return 0; > return __folio_lock_fault(folio, vmf); > } > > Then the users look like ... > > > @@ -3580,8 +3581,10 @@ static vm_fault_t remove_device_exclusive_entry(= struct vm_fault *vmf) > > if (!folio_try_get(folio)) > > return 0; > > > > - if (!folio_lock_or_retry(folio, vma->vm_mm, vmf->flags)) { > > + if (!folio_lock_or_retry(folio, vma, vmf->flags, &lock_dropped)) = { > > folio_put(folio); > > + if (lock_dropped && vmf->flags & FAULT_FLAG_VMA_LOCK) > > + return VM_FAULT_VMA_UNLOCKED | VM_FAULT_RETRY; > > return VM_FAULT_RETRY; > > } > > ret =3D folio_lock_fault(folio, vmf); > if (ret) > return ret; > > > @@ -3837,9 +3840,9 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > > goto out_release; > > } > > > > - locked =3D folio_lock_or_retry(folio, vma->vm_mm, vmf->flags); > > - > > - if (!locked) { > > + if (!folio_lock_or_retry(folio, vma, vmf->flags, &lock_dropped)) = { > > + if (lock_dropped && vmf->flags & FAULT_FLAG_VMA_LOCK) > > + ret |=3D VM_FAULT_VMA_UNLOCKED; > > ret |=3D VM_FAULT_RETRY; > > goto out_release; > > } > > ret |=3D folio_lock_fault(folio, vmf); > if (ret & VM_FAULT_RETRY) > goto out_release; > > ie instead of trying to reconstruct what __folio_lock_fault() did from > its outputs, we just let folio_lock_fault() tell us what it did. Thanks for taking a look! Ok, I think what you are suggesting is to have a new set of folio_lock_fault()/__folio_lock_fault() functions which return vm_fault_t directly, __folio_lock_fault() will use __folio_lock_or_retry() internally and will adjust its return value based on __folio_lock_or_retry()'s return and the lock releasing rules described in the comments for __folio_lock_or_retry(). Is my understanding correct?