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Thu, 27 Feb 2025 08:47:30 -0800 (PST) MIME-Version: 1.0 References: <20250218181656.207178-1-fvdl@google.com> <20250218181656.207178-11-fvdl@google.com> <20250226180900.GA1042@cmpxchg.org> In-Reply-To: <20250226180900.GA1042@cmpxchg.org> From: Frank van der Linden Date: Thu, 27 Feb 2025 08:47:18 -0800 X-Gm-Features: AQ5f1Jq4MYeH7gOFJQGJ71-iV_kaHKELQA_gD8gPyEFnkP_235vGg7zbJImj8JA Message-ID: Subject: Re: [PATCH v4 10/27] mm/sparse: allow for alternate vmemmap section init at boot To: Johannes Weiner Cc: akpm@linux-foundation.org, muchun.song@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, yuzhao@google.com, usamaarif642@gmail.com, joao.m.martins@oracle.com, roman.gushchin@linux.dev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Stat-Signature: tezt5xkfucg9cgaqarmtrrg56cznfzf1 X-Rspamd-Queue-Id: AEC3240027 X-Rspamd-Server: rspam07 X-HE-Tag: 1740674851-507506 X-HE-Meta: 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 0OEbZNkc IH1jUlYQNsZahL8mti3ZULd3T1NVo6fwS+u6JI8e3QVfCBF0976v9/GRJZyKl4DNOSbspVWIcHSOzKU3WEi+sjwZIRLtgP+AAtqi/4QYIDVj61kj595l1xcAreUCyr8dtLZMSud1DF+0SZbRzu4ZVrqqelNaVEEnpANW2jB03Wb2uZACWclkI4lpz2r7AqJoExgzmvuTnA4kzI4qpxA4mDXgCt5FlPgKGT/EBxvTQc4wkp1kiH08w5G5eh7rLgPA9aAqa 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, Feb 26, 2025 at 10:09=E2=80=AFAM Johannes Weiner wrote: > > On Tue, Feb 18, 2025 at 06:16:38PM +0000, Frank van der Linden wrote: > > @@ -489,6 +489,14 @@ config SPARSEMEM_VMEMMAP > > SPARSEMEM_VMEMMAP uses a virtually mapped memmap to optimise > > pfn_to_page and page_to_pfn operations. This is the most > > efficient option when sufficient kernel resources are available= . > > + > > +config ARCH_WANT_SPARSEMEM_VMEMMAP_PREINIT > > + bool > > + > > +config SPARSEMEM_VMEMMAP_PREINIT > > + bool "Early init of sparse memory virtual memmap" > > + depends on SPARSEMEM_VMEMMAP && ARCH_WANT_SPARSEMEM_VMEMMAP_PREIN= IT > > + default y > > oldconfig just prompted me on this, but it's not clear to me what it > does. Not even after skimming the changelog of the patch to be honest. > > Can you please add a help text that explains the user-visible effects > of the toggle, as well as guidance as to who might care to change it? Hi Johannes, Thanks for your comment. How's this: =3D=3D Enables subsystems to pre-initialize memmap in their own way, allowing for memory savings during boot. The HugeTLB code uses this to initialize memmap for bootmem allocated gigantic hugepages in a way that is done by HUGETLB_PAGE_OPTIMIZE_VMEMMAP. This means saving this memory right away, instead of allocating it first and then freeing it later. Not allocating these pages at all during boot allows for specifying a bigger number of hugepages on the kernel commandline on larger systems. =3D=3D - Frank