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dkim=pass header.d=Nvidia.com header.s=selector2 header.b=mfg3n2r2; dmarc=pass (policy=reject) header.from=nvidia.com; spf=none (imf15.hostedemail.com: domain of jhubbard@nvidia.com has no SPF policy when checking 40.107.102.54) smtp.mailfrom=jhubbard@nvidia.com X-Stat-Signature: yf88km61yy7roator4gewp9pg1zyx8ot X-HE-Tag: 1643659316-610757 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 1/31/22 04:05, Jan Kara wrote: > On Sun 30-01-22 21:17:52, John Hubbard wrote: >> Unraveling the rat's nest set of APIs in mm/gup.c a bit more. >> get_user_pages_locked() was not helping at all, so remove it. >> >> Also, lookup_node() has only a single caller, but it is still worth >> having a clearer locking policy there. Changing it so that the caller >> both takes and releases the mmap_lock, thus leaving lookup_node() with >> the sole job of translating a virtual address into a numa node ID. >> >> Signed-off-by: John Hubbard > > Well, the point of _locked() GUP variants is that we can unlock mmap_sem > when reading a page from the disk during a page fault (hidden behind > VM_FAULT_RETRY). So as such _locked() variants are about reducing mmap_sem > latency rather than code readability. In this particular case, I don't > think using _locked() variant in lookup_node() is very beneficial > (generally I would not expect to take a fault there) but at least a > justification in the commit message should be different :). > > Honza I'll rewrite this commit description to cover this point properly. Jason also suggested using gup-fast, which I like. thanks, -- John Hubbard NVIDIA