From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 44BDDC61DD3 for ; Tue, 1 Sep 2026 10:17:11 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 4134C6B00B4; Tue, 1 Sep 2026 06:17:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 3EBD06B00B7; Tue, 1 Sep 2026 06:17:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 300806B00B8; Tue, 1 Sep 2026 06:17:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id E575A6B00B4 for ; Tue, 1 Sep 2026 06:17:09 -0400 (EDT) Received: from smtpin12.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay09.hostedemail.com (Postfix) with ESMTP id 3ED2D802DD for ; Tue, 1 Sep 2026 10:17:09 +0000 (UTC) X-FDA: 85164790578.12.86FF38B Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by imf17.hostedemail.com (Postfix) with ESMTP id 72CD440008 for ; Tue, 1 Sep 2026 10:17:07 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kDGR8P53; spf=pass (imf17.hostedemail.com: domain of vbabka@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1788257827; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=PDWASibxaGJJhiXNV7zhT5m/05R5Tf7kS7Q31f7HJsM=; b=A9dNyh5lzEKdJoSTPt3304G4iCPCTONJrz+IOKQEzmsFpywq+h9gv+PskUtH90qRo5Qo4w AK3xgQiVLhfMP7Fd303KXO1ph8OEvMR6sMIKMfQmNB979ZQxNS+Hra7424BOKGq4BBIkha 7YbrH3por4ypX7iU+9J58qNoOBHm/1U= ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1788257827; b=8AsE55YVHeF6fIItfVv1TdBd4DmQ5nF7+ziM4h7jtDuHLmtcs07T9Nrjc5cKx+qV2lavzY kcgPX5z8wJejRkLGFTZvUlduGsDHnDc5GxqXJeECldYzIySSjxSHLGKXzj5eTxgoXE8PCi BfebeJCMMm/ZwEFHbEhZPspBR/wO+Ag= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=kDGR8P53; spf=pass (imf17.hostedemail.com: domain of vbabka@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=vbabka@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by tor.source.kernel.org (Postfix) with ESMTP id D380C60200; Tue, 1 Sep 2026 10:17:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 190D81F000E9; Tue, 1 Sep 2026 10:17:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788257826; bh=PDWASibxaGJJhiXNV7zhT5m/05R5Tf7kS7Q31f7HJsM=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=kDGR8P53xawEBJdeOMODGSJcHWXW9PTRwe4zSvQErRx0xNSPPxmDixKdD7kQv64cf +SPu/Xh+GhaFnkV8gbTgIR+sQ0yl6gyMClPAcCGvkk8BP7vaZCTXTu4in3CN8iwiUI OcUAAlj5xchiqvlqiQ0erXY5DpTTSViTxWEuAAv4eDmcBjLZFC5/CU3KlriFWZH9jw 9Eaa/DDy9jIkQ1Oa4HEP9AjMXXtBMv8WwOdn7PjkDafjRFKo7r8wHkFD7htgVnBq/t P4XKi3Q+YY+4+TS+pxW3+tqVHZNWeT0/Kt/ScgU0Ieg9QSUGncB41SjWa58oNc6zAJ Z9Nbl7tSBfWhw== Message-ID: <23db34a1-ba1b-495d-91ea-18419e0dc8df@kernel.org> Date: Tue, 1 Sep 2026 12:17:02 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/2] docs/core-api: memory-allocation: add k[mz]alloc_obj() and clarify kmalloc To: "Mike Rapoport (Microsoft)" , Jonathan Corbet , Andrew Morton , David Hildenbrand Cc: "Liam R. 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 References: <20260831-docs-memalloc-guide-v1-0-547718c274c1@kernel.org> <20260831-docs-memalloc-guide-v1-1-547718c274c1@kernel.org> From: "Vlastimil Babka (SUSE)" Content-Language: en-US Autocrypt: addr=vbabka@kernel.org; keydata= xsFNBFZdmxYBEADsw/SiUSjB0dM+vSh95UkgcHjzEVBlby/Fg+g42O7LAEkCYXi/vvq31JTB KxRWDHX0R2tgpFDXHnzZcQywawu8eSq0LxzxFNYMvtB7sV1pxYwej2qx9B75qW2plBs+7+YB 87tMFA+u+L4Z5xAzIimfLD5EKC56kJ1CsXlM8S/LHcmdD9Ctkn3trYDNnat0eoAcfPIP2OZ+ 9oe9IF/R28zmh0ifLXyJQQz5ofdj4bPf8ecEW0rhcqHfTD8k4yK0xxt3xW+6Exqp9n9bydiy tcSAw/TahjW6yrA+6JhSBv1v2tIm+itQc073zjSX8OFL51qQVzRFr7H2UQG33lw2QrvHRXqD Ot7ViKam7v0Ho9wEWiQOOZlHItOOXFphWb2yq3nzrKe45oWoSgkxKb97MVsQ+q2SYjJRBBH4 8qKhphADYxkIP6yut/eaj9ImvRUZZRi0DTc8xfnvHGTjKbJzC2xpFcY0DQbZzuwsIZ8OPJCc LM4S7mT25NE5kUTG/TKQCk922vRdGVMoLA7dIQrgXnRXtyT61sg8PG4wcfOnuWf8577aXP1x 6mzw3/jh3F+oSBHb/GcLC7mvWreJifUL2gEdssGfXhGWBo6zLS3qhgtwjay0Jl+kza1lo+Cv BB2T79D4WGdDuVa4eOrQ02TxqGN7G0Biz5ZLRSFzQSQwLn8fbwARAQABzSNWbGFzdGltaWwg QmFia2EgPHZiYWJrYUBrZXJuZWwub3JnPsLBsAQTAQoAWhYhBKlA1DSZLC6OmRA9UCJPp+fM gqZkBQJqFFy6GxSAAAAAAAQADm1hbnUyLDIuNSsxLjEyLDIsMgIbAwUJGtCBUAULCQgHAwUV CgkICwUWAgMBAAIeBQIXgAAKCRAiT6fnzIKmZJIUEADFx/tREzUImHrEwVHeSvDFmA7tJysI UVrlvrM09E7GIuzphzv7jYmo8n3ANpCczLEVr4G0syYQdTigaZgv3+FQDIIzhKih1IHhu1Ei XHlywNWKnQxxQEUNi5Mwx43wQz5XVw9F1A7gtKBKNtfogO511hAbrzagrYajyQacEJ/+sfhZ 9Da8ltHIXD8pcYaHUfQgEusCgmEd9+KrUwrTbckFKmYq5chuE6yJ4J0EmWknL096jIE6CnzF FRslQ3B1UKDjxVsm1ZHfir5NeWszLkTvGFsddFaWTgh8UycESG6VQzKXjjewXu2pG7YQYRpj QKm1W5X2TkwWkXRBZTmfmbhxIUMh3+zf5wQ463rSmDN/8v81tdqBtAW6rH/kzg1GvkaTHXn0 507yEHFzBksk2viAuIxxr7km8+/KARYLIdGtx30EG8cKzAUZOK6WqxtNCsXUJNrVE8CWrCaD icoNu7Fs1c5hmPHdSTnU48ce67449DdnO4neLSNhRiGlMHJgfJUmgrxu/hcYeOZ3haWmEQ2w uW1Mh01OHi8QZHCEyAbABrPs9GUgccc/4eYXX9hIgxfSkYzn8f+8NuIFPWl/0uTvjgqU29FQ SbzOLxHq9439Ox40G5mS5eZXRGxITYR+6TXvRGI6P/264jvflnr/pDGUttaikU+0W+1uxgKH cmYbEc7ATQRbGTU1AQgAn0H6UrFiWcovkh6EXVcl+SeqyO6JHOPm+e9Wu0Vw+VIUvXZVUVVQ La1PQDUi6j00ChlcR66g9/V0sPIcSutacPKfdKYOBvzd4rlhL8rfrdEsQw5ApZxrA8kYZVMh FmBRKAa6wos25moTlMKpCWzTH84+WO5+ziCTsTUZASAToz3RdunTD+vQcHj0GqNTPAHK63sf bAB2I0BslZkXkY1RLb/YhuA6E7JyEd2pilZOrIuBGl/5q2qSakgnAVFWFBR/DO27JuAksYnq +aH8vI0xGvwn75KqSk4UzAkDzWSmO4ZHuahKtQgZNsMYV+PGayRBX9b9zbldzopoLBdqHc4n jQARAQABwsF8BBgBCgAmAhsMFiEEqUDUNJksLo6ZED1QIk+n58yCpmQFAmfIHFQFCRYU6J8A CgkQIk+n58yCpmS2PA//bqN1LfcotmArgElsa+0EGZSQlYgK48pm8WAeTXTngudP9IJ4SuKY HR5RNjHcBeqN+Me0zxRqYzRb8nGanHEkDyf4Im8DQM8d6vbyU+FcPmG4skud4kgS1zMHnlVd SXfSIwKC/hKgdHG8aBV7545Lz9X6Iohea+94wneD0aw/hqF+QWewGZhWJriWAZtvEkzNjQOi 4U9F/trLten/x7bpphDSnDMKJtITbtzATT1Dq7o7VpIUK1nCTQALMuMjKCdi8OdU/+V+R3O4 0PXWvX8qrvqYapVbZ+9KqT74FsuB0Ya9uXwgBF2Q6cRuETZk5vqaqKxzqoQZCO8AOz/58j6O 2RHNy/mZEN+7tJ5Tsq42zVJ4jxsT8b9YplavCMsnBgDeRWhcbYhCyttoL7nYISyWg4kQYZ/P wIV3OuNv2f8iKYsxNsRuClOAF82+gvqOy1/1pprFjy8uo2pkoOrb63aOP3vO5VHnRKgra6dq NcaZ+c6J4H+nEJGi2SkHAUJz5oBzuThvPudLvPA/SK8sKoM01IRxSihev/S/5WLazXB1PGem OCbvzC1IjWJJraxiDJ5IygokapUa2RP7+WBR22skQ3SSl6G107QgWKSyTOGWEaRmV53vxQLV jXuCmzSSasTL60zq5yGrT4/DYQVSNEUiUbG4pYekxJujNeEDkUlky0Y= In-Reply-To: <20260831-docs-memalloc-guide-v1-1-547718c274c1@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: xkzcae4tjc8rspyihtbk3mtagir1y65i X-Rspamd-Queue-Id: 72CD440008 X-Rspamd-Server: rspam02 X-Rspam-User: X-HE-Tag: 1788257827-473712 X-HE-Meta: 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 OqMkQD/w f6uD6znAwBjqNsZMODW0NW08ikrVYn4YvCceYRbSXpKChfribxviwTIngkAQAg6cUKlgMCKEhhM/v/PADQX4fsKPv9cmDYQiNS1ppYeJrqXmdAVL4vFX7s7YbSFXNvow5sLNhg9QlvtNz39cZBVLFhEfsrOeNdCRN2pizBlZz5zhzTZC/L2RKGRDRhuLKU/ZRm8ULi1EE31BrPcC/U8XAT00TZUrfGGAZQzsWLLFqkpo4ANCntbYq5HE/ynoZ4dq0ucEEv7/tjg6VZfBzpIArlneEpfzHy9vj6eqBILOfLBYNQenrXtT6Sf7TBBu+7StL2M2/EwUPwoZPKrY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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) Suggestion below: > --- > Documentation/core-api/memory-allocation.rst | 30 +++++++++++++++++++++------- > 1 file changed, 23 insertions(+), 7 deletions(-) > > diff --git a/Documentation/core-api/memory-allocation.rst b/Documentation/core-api/memory-allocation.rst > index 0f19dd5243239..8ecfa4d35f4f5 100644 > --- a/Documentation/core-api/memory-allocation.rst > +++ b/Documentation/core-api/memory-allocation.rst > @@ -19,6 +19,12 @@ Diversity of the allocation APIs combined with the numerous GFP flags > makes the question "How should I allocate memory?" not that easy to > answer, although very likely you should use > > +:: > + > + kzalloc_obj(); > + > +or > + > :: > > kzalloc(, GFP_KERNEL); > @@ -139,10 +145,13 @@ allocate memory for an array, there are kmalloc_array() and kcalloc() > helpers. The helpers struct_size(), array_size() and array3_size() can > be used to safely calculate object sizes without overflowing. > > -The maximal size of a chunk that can be allocated with `kmalloc` is > -limited. The actual limit depends on the hardware and the kernel > -configuration, but it is a good practice to use `kmalloc` for objects > -smaller than page size. > +Since 7.0 there are type aware kmalloc-family helpers that let you safely and > +conveniently allocate a single object or arrays of objects with kzalloc_obj() > +and kmalloc_obj() and their array versions kzalloc_objs() and > +kmalloc_objs(). These helpers only need the type of the object that should be > +allocated and the count of elements in the array for the array versions. > + > +As of v7.2, vast majority of the memory allocations use kzalloc_obj(). > > The address of a chunk allocated with `kmalloc` is aligned to at least > ARCH_KMALLOC_MINALIGN bytes. For sizes which are a power of two, the > @@ -154,9 +163,16 @@ Chunks allocated with kmalloc() can be resized with krealloc(). Similarly > to kmalloc_array(): a helper for resizing arrays is provided in the form of > krealloc_array(). > > -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? (Also `MAX_ORDER` doesn't exist anymore) > +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 >