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Wed, 28 Jan 2026 20:45:03 -0800 (PST) MIME-Version: 1.0 References: <20260128225648.2938636-1-greenjustin@chromium.org> In-Reply-To: From: Arjun Roy Date: Wed, 28 Jan 2026 20:44:52 -0800 X-Gm-Features: AZwV_QjAbJkkQHwHrEr3D9jthPjbfPNMN8oX-3O0cJ2iI8x4OxtVeO-g9n7NlYA Message-ID: Subject: Re: [PATCH] mm: Refactor vma_map_pages to use vm_insert_pages To: Matthew Wilcox Cc: Brian Geffon , Justin Green , akpm@linux-foundation.org, linux-mm@kvack.org, david@kernel.org, lorenzo.stoakes@oracle.com, Liam.Howlett@oracle.com, vbabka@suse.cz, rppt@kernel.org, surenb@google.com, mhocko@suse.com, linux-kernel@vger.kernel.org, greenjustin@google.com, rientjes@google.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: C8D09140008 X-Rspam-User: X-Rspamd-Server: rspam05 X-Stat-Signature: 78rnd94jttc591ozxa9etggxdt679cfz X-HE-Tag: 1769661904-821430 X-HE-Meta: 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 AY3mcy2i jfWvxwZcx9jPrRoPNYaDSntA84hoOgHb637QYs2pV8U4EngAGxQ9VYnPykpUxG4DJ3IxwQ3+hgYQK1LR+0OryE5XD9whzuJx/aOq5skO5f97k3W/vHl0XTvCm180GW92CDrvKh3vOOSOLSCHSe7xXHgD3Aeip7yISwjCwLTUyZTsmnOuF6ztmKqeU6EnhS8GajjQ6bYBqzIxXhJi/5LavH05MVE5/0gvtSibiw5Bajau9nbWuXu1fD63OoFIO9Z3OcITNjsK0Pr5mpM7H9SOFqZlWBDHOgEEYUe83d+bs6Vi/GtR4/Qf68/ZgGkRIp5Kk+ZBRebU53I/Cit7XnNgRzEMY6mZyMZhpCTzK+wTv39Bt0u7GbHox3GlJOf8qQquD+YZPSdFQRzlB8Pg= 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: List-Subscribe: List-Unsubscribe: On Wed, Jan 28, 2026 at 4:51=E2=80=AFPM Matthew Wilcox wrote: > > On Wed, Jan 28, 2026 at 05:59:12PM -0500, Brian Geffon wrote: > > On Wed, Jan 28, 2026 at 5:57=E2=80=AFPM Justin Green wrote: > > > > > > vma_map_pages currently calls vm_insert_page on each individual page = in > > > the mapping, which creates significant overhead because we are > > > repeatedly spinlocking. Instead, we should batch insert pages using > > > vm_insert_pages, which amortizes the cost of the spinlock. > > > > This makes sense, I wonder why this wasn't done previously? > > That's always a good question, because it might reveal why this patch is > a bad idea ... > > However in this case, it simply seems to be an oversight. > __vm_map_pages() was introduced in May 2019 and then vm_insert_pages() > was added in April 2020. > Yes, it was an oversight. I had originally cooked up vm_insert_pages() to amortize that spinlock for TCP zerocopy receive, and had not noticed __vm_map_pages(= ) sitting right there. Reviewed-by: Arjun Roy -Arjun > Reviewed-by: Matthew Wilcox (Oracle)