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[35.245.167.64]) by smtp.gmail.com with ESMTPSA id 71dfb90a1353d-5ee3243e30fsm81430e0c.9.2026.11.12.07.00.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 12 Nov 2026 07:00:35 -0800 (PST) X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 12 Nov 2026 10:00:34 -0500 Message-Id: Cc: "Alexander Graf" , "Andrew Morton" , "Chen Pei" , "George Guo" , "Kexin Liu" , "Randy Dunlap" , "Shuah Khan" , "Sourabh Jain" , , , , Subject: Re: [PATCH v3 5/5] kho: docs: update description of bootmem regions From: "Pasha Tatashin" To: "Mike Rapoport (Microsoft)" , "Jonathan Corbet" , "Pasha Tatashin" , "Pratyush Yadav" X-Mailer: aerc 0.22.0-39-g5d7784875be2 References: <20261112-kho-bootmem-sizing-v3-0-f0c8d00295d5@kernel.org> <20261112-kho-bootmem-sizing-v3-5-f0c8d00295d5@kernel.org> In-Reply-To: <20261112-kho-bootmem-sizing-v3-5-f0c8d00295d5@kernel.org> On Thu Nov 12, 2026 at 5:38 AM EST, Mike Rapoport (Microsoft) wrote: > The description of the boot memory regions does not mention the low > memory region and claims there is always a region per node plus a global > region, while the low memory and the global regions are not allocated > when they would be empty. > > List all types of the boot memory regions and describe when they are not > allocated. > > While on it, fix grammar and split the description of the regions size > and of the CMA usage into separate paragraphs. > > Signed-off-by: Mike Rapoport (Microsoft) > --- > Documentation/core-api/kho/index.rst | 31 ++++++++++++++++++++----------= - > 1 file changed, 20 insertions(+), 11 deletions(-) > > diff --git a/Documentation/core-api/kho/index.rst b/Documentation/core-ap= i/kho/index.rst > index e78a2bbe2be1d..ce2bf9cf66514 100644 > --- a/Documentation/core-api/kho/index.rst > +++ b/Documentation/core-api/kho/index.rst > @@ -52,17 +52,26 @@ allocations before during boot up to the initializati= on of the page allocator. > =20 > We guarantee that we always have such regions through the boot memory re= gions: > On first boot KHO allocates several physically contiguous memory regions= . Since > -after kexec these regions will be used by early memory allocations, ther= e is a > -boot memory region per NUMA node plus a boot memory region to satisfy > -allocations requests that do not require particular NUMA node assignment= . By > -default, size of the boot memory region is calculated based on amount of= memory > -allocated during boot. The ``kho_bootmem`` kernel command line option ma= y be > -used to explicitly define size of the boot memory regions. The boot memo= ry > -regions are declared as CMA when page allocator is initialized so that t= heir > -memory can be used during system lifetime. CMA gives us the guarantee th= at no > -handover pages land in that region, because handover pages must be at a = static > -physical memory location and CMA enforces that only movable pages can be= located > -inside. > +after kexec these regions will be used by early memory allocations, ther= e are > +several types of such regions to ensure that all boot-time allocations w= ork: > + > +* a low memory region for allocations below ``ARCH_LOW_ADDRESS_LIMIT`` > +* a region per NUMA node > +* a global region for allocations that do not require a particular NUMA = node > + > +Regions that would be empty are not allocated. For example, there is no = low > +memory region when ``ARCH_LOW_ADDRESS_LIMIT`` covers all memory, and the= re is > +no global region when ``CONFIG_NUMA`` is disabled. > + > +By default, the size of the boot memory regions is calculated based on t= he > +amount of memory allocated during boot. The ``kho_bootmem`` kernel comma= nd line > +option may be used to explicitly define the size of the boot memory regi= ons. > + > +The boot memory regions are declared as CMA when the page allocator is > +initialized so that their memory can be used during system lifetime. CMA= gives > +us the guarantee that no handover pages land in that region, because han= dover > +pages must be at a static physical memory location and CMA enforces that= only > +movable pages can be located inside. > =20 > After KHO kexec, we ignore the ``kho_bootmem`` kernel command line optio= n and > instead reuse the exact same region that was originally allocated. This = allows Reviewed-by: Pasha Tatashin =20 --=20 Pasha