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Howlett" , Lorenzo Stoakes , Michal Hocko , Randy Dunlap , Shuah Khan , Suren Baghdasaryan , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: Re: [PATCH 1/2] docs/core-api: memory-allocation: add k[mz]alloc_obj() and clarify kmalloc Message-ID: References: <20260831-docs-memalloc-guide-v1-0-547718c274c1@kernel.org> <20260831-docs-memalloc-guide-v1-1-547718c274c1@kernel.org> <23db34a1-ba1b-495d-91ea-18419e0dc8df@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <23db34a1-ba1b-495d-91ea-18419e0dc8df@kernel.org> X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 3E008C0014 X-Stat-Signature: 5o4okjhs8656ds41eya1d5qy3f95da6o X-HE-Tag: 1788279030-774953 X-HE-Meta: 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 fjQkZXLM jSOqowZMferkJQFUZ7CKL+VY5EjO/5oBfEW9zufNDAwQeHy7HsO2SMql/qbi0JooOobZmE11YRjI3wnTGkBEw8IECt0H2Fj/5/GjTbcpfNKQZY2ImzRffsFlTOzObwgGCu2GpRONmppXhH6EFU2uH8hdXheyK82xXQ8/pkeVQIl9E7MvYWcTP1qt9j2FhJ0SPUfyPIZ1XlCD4tfTim/0fj6RUgI1/f+yqDVNUF3Z8By8n+7hcD0As7zF8AdgI0u64xAqFn11lCbHQYWBSqA5mp+xLDs0iVSUEzCZK4WIjh2ygl4iJCObvwEA3Rw02aKxffT4dtrzvZD0cZ0c= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Sep 01, 2026 at 12:17:02PM +0200, Vlastimil Babka (SUSE) wrote: > On 8/31/26 17:13, Mike Rapoport (Microsoft) wrote: > > Since v7.0 the most used memory allocation function is kzalloc_obj(). > > > > Update hte memory-allocation guide to describe k[mz]alloc_obj() family > > and make kzalloc_obj() the first answer to "How should I allocate > > memory?" question. > > > > While on it, clarify description of kmalloc() size limitations. > > > > Signed-off-by: Mike Rapoport (Microsoft) > > Acked-by: Vlastimil Babka (SUSE) Thanks! > Suggestion below: > > > --- > > Documentation/core-api/memory-allocation.rst | 30 +++++++++++++++++++++------- > > 1 file changed, 23 insertions(+), 7 deletions(-) > > > > -For large allocations you can use vmalloc() and vzalloc(), or directly > > -request pages from the page allocator. The memory allocated by `vmalloc` > > -and related functions is not physically contiguous. > > +`kmalloc` always allocates physically contiguous memory and the maximal size of > > +a chunk that can be allocated with `kmalloc` is limited by `MAX_ORDER`, the > > +same limit also applies to the page allocator. > > Would it be better to say the maximal size is KMALLOC_MAX_SIZE which is > derived from page allocator's MAX_PAGE_ORDER? My point was that whenever you allocate with kmalloc() the limit is MAX_PAGE_ORDER, not necessarily for actual slab allocations. > (Also `MAX_ORDER` doesn't exist anymore) Will fix. > > +Internally, slab allocator differentiates allocations of different orders and > > +delegates larger allocations to the page allocator, but for the users of > > +`kmalloc` family it is entirely transparent. > > + > > +For large allocations that do not require physically contiguous memory you can > > +use vmalloc() and vzalloc() family. > > > > If you are not sure whether the allocation size is too large for > > `kmalloc`, it is possible to use kvmalloc() and its derivatives. It will > > > -- Sincerely yours, Mike.