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Fri, 14 Apr 2023 11:32:19 -0700 (PDT) MIME-Version: 1.0 References: <20230414180043.1839745-1-surenb@google.com> In-Reply-To: <20230414180043.1839745-1-surenb@google.com> From: Suren Baghdasaryan Date: Fri, 14 Apr 2023 11:32:08 -0700 Message-ID: Subject: Re: [PATCH 1/1] mm: handle swap page faults if the faulting page can be locked To: akpm@linux-foundation.org Cc: willy@infradead.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, 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-Rspamd-Server: rspam03 X-Stat-Signature: yib5159kedng5grc6m59q99tb8dbgqh4 X-Rspamd-Queue-Id: 42EF08000D X-HE-Tag: 1681497140-676090 X-HE-Meta: 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 27n9L2WF TMdTuRJCu2VfjPdWNJQUTF6W0HSNgGswcdJ26Zjef/PAUAjyAOGFu5Du6tQ/AGms4RTFDNIWxfEcW/vf+4QmHEffDNKCGiBDSH0HclXsBtt5UmMbYYd9YMiLUi7BKdAsIAgZyfHztd1E+dFAq/Ioxc/zwbYB9VZn1n38mG7ZWC6afiJ/UWPcPrcuUGX/mWia2M8ZDXHHPlHvfTYuDN/R/VXnxWcJ78HeNNATfMg0oRxF0qudnMXR8PmioRCSFAIejTUoP4yw+aJZ2NO8= 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, Apr 14, 2023 at 11:00=E2=80=AFAM Suren Baghdasaryan wrote: > > When page fault is handled under VMA lock protection, all swap page > faults are retried with mmap_lock because folio_lock_or_retry > implementation has to drop and reacquire mmap_lock if folio could > not be immediately locked. > Instead of retrying all swapped page faults, retry only when folio > locking fails. I just realized that the title of the patch is misleading. It's about handling page fault under VMA lock. A better title would be something like: "mm: handle swap page faults under vma lock if page is uncontended" > > Signed-off-by: Suren Baghdasaryan > --- > Patch applies cleanly over linux-next and mm-unstable > > mm/filemap.c | 6 ++++++ > mm/memory.c | 5 ----- > 2 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index 6f3a7e53fccf..67b937b0f436 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -1706,6 +1706,8 @@ static int __folio_lock_async(struct folio *folio, = struct wait_page_queue *wait) > * mmap_lock has been released (mmap_read_unlock(), unless flags had= both > * FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_RETRY_NOWAIT set, in > * which case mmap_lock is still held. > + * If flags had FAULT_FLAG_VMA_LOCK set, meaning the operation is pe= rformed > + * with VMA lock only, the VMA lock is still held. > * > * If neither ALLOW_RETRY nor KILLABLE are set, will always return true > * with the folio locked and the mmap_lock unperturbed. > @@ -1713,6 +1715,10 @@ static int __folio_lock_async(struct folio *folio,= struct wait_page_queue *wait) > bool __folio_lock_or_retry(struct folio *folio, struct mm_struct *mm, > unsigned int flags) > { > + /* Can't do this if not holding mmap_lock */ > + if (flags & FAULT_FLAG_VMA_LOCK) > + return false; > + > if (fault_flag_allow_retry_first(flags)) { > /* > * CAUTION! In this case, mmap_lock is not released > diff --git a/mm/memory.c b/mm/memory.c > index d88f370eacd1..3301a8d01820 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -3715,11 +3715,6 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > if (!pte_unmap_same(vmf)) > goto out; > > - if (vmf->flags & FAULT_FLAG_VMA_LOCK) { > - ret =3D VM_FAULT_RETRY; > - goto out; > - } > - > entry =3D pte_to_swp_entry(vmf->orig_pte); > if (unlikely(non_swap_entry(entry))) { > if (is_migration_entry(entry)) { > -- > 2.40.0.634.g4ca3ef3211-goog >