From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EC5A830D40C; Mon, 13 Jul 2026 16:37:44 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783960666; cv=none; b=r33t1NOch1YBaLZxhX6IwHYvJvc8M6ThwFdHFwYer8hYKVfM8A/L0gEBJRJRnFxA82rVfYP2POCPXtE/yKKgVZg9tbnHAQZ98Que0VoAne1NvnRKxbw80cHtn2l6YM2FswR7A7BvhVKpusu9jhIghSH1um7qUPuqpep7WRbA330= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783960666; c=relaxed/simple; bh=UbeYdzfhxoc5Kcmm6E7bqN048H0LB9WUkgbJGm0NuBs=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=FWKGQBI4c52wCZ7VQ2dS8WYqg/I8yHHfFQEGeTsRzzZ3LWCwtvQaspk9hohVjjkz91aNQLE/t8ai/DRFztb87J9gK/kouRTrHjq0AvCCzhP+S7iidL9eISG7s+zJczNJ0GIunOUXYZtGIql/cGVEwIKVawFQ0Cjn2xAKXNaAFrc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=EMKYsEWE; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="EMKYsEWE" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C8111F000E9; Mon, 13 Jul 2026 16:37:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783960664; bh=u/P4qKRpyyO/IqxmO4MioJCCSc/ZdvDZK4M5KJUmWHU=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=EMKYsEWECwFyZOLAzrrUyIkqBqCAe/QiyW4dkMgZe21P2CsUOXzfyU8/5Kg4sMutT CtgooL5RszapnkM2tGGpI2kRftv9v7OORyRGUrCp+C98Zl7iohEzKFoiCTYcj7sz4G TTY17PEtXBfqDPGovkUYPjGGf+NIt2Zk2akuw5x/uv09CvzuCkpq2kvizw8CJSK3ud mjKj7Am+v4uOApq6IlDDpQmLVUCajMTcOkkty0mOAAtSGW3PMyWUljcq1bjAw0MnF3 LlpsRbt3Thds+4gl/xEfTujN5gWBqFX3PnWbAfGwtGSRCnyLYUHlx2KJW5ggdtuBuK bRtJUPBnzmXqA== Message-ID: <0e7c2aff-a278-4118-a9a9-123c2735ed67@kernel.org> Date: Mon, 13 Jul 2026 18:37:35 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v5 13/18] mm: Remove __alloc_pages_node() Content-Language: en-US To: Zi Yan , Brendan Jackman Cc: Brendan Jackman , Andrew Morton , Suren Baghdasaryan , Michal Hocko , Johannes Weiner , Muchun Song , Oscar Salvador , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Matthew Brost , Joshua Hahn , Rakie Kim , Byungchul Park , Ying Huang , Alistair Popple , Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt , "Harry Yoo (Oracle)" , Gregory Price , Alexei Starovoitov , Matthew Wilcox , Hao Ge , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, derkling@google.com, reijiw@google.com, Yosry Ahmed References: <20260703-alloc-trylock-v5-0-c87b714e19d3@google.com> <20260703-alloc-trylock-v5-13-c87b714e19d3@google.com> <399958F1-544F-4826-90E5-B471E2231375@nvidia.com> From: "Vlastimil Babka (SUSE)" 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: <399958F1-544F-4826-90E5-B471E2231375@nvidia.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/13/26 17:54, Zi Yan wrote: > On 13 Jul 2026, at 11:26, Brendan Jackman wrote: > >> On Fri Jul 3, 2026 at 2:57 PM UTC, Zi Yan wrote: >>> On Fri Jul 3, 2026 at 8:31 AM EDT, Brendan Jackman wrote: >>>> There were only a few users, which have been removed. The only advantage >>>> of this API over alloc_pages_node() is avoiding a single conditional >>>> branch. The disadvantages are: >>>> >>>> 1. More API surface, more sources of confusion, more maintenance. >>>> >>>> 2. Worse impact of CPU hotplug bugs: most users of __alloc_pages_node() >>>> were using the result of cpu_to_node(); if the CPU gets hotplugged >>>> out this will return NUMA_NO_NODE. If one of these paths fails to >>>> protect against a concurrent hotplug then page_alloc.c will use >>>> NUMA_NO_NODE as an index into NODE_DATA() and cause some horrible >>>> memory corruption or other. With alloc_pages_node(), the code might >>>> just work fine. >>>> >>>> Ulterior motive: this frees up the __* variants of the allocator APIs to >>>> serve specifically for use as mm-internal API. >>>> >>>> Reviewed-by: Suren Baghdasaryan >>>> Reviewed-by: Vlastimil Babka (SUSE) >>>> Signed-off-by: Brendan Jackman >>>> --- >>>> include/linux/gfp.h | 20 ++++---------------- >>>> 1 file changed, 4 insertions(+), 16 deletions(-) >>>> >>>> diff --git a/include/linux/gfp.h b/include/linux/gfp.h >>>> index 01d6d2591f49e..3bf55a5f9143e 100644 >>>> --- a/include/linux/gfp.h >>>> +++ b/include/linux/gfp.h >>>> @@ -256,21 +256,6 @@ static inline void warn_if_node_offline(int this_node, gfp_t gfp_mask) >>>> dump_stack(); >>>> } >>>> >>>> -/* >>>> - * Allocate pages, preferring the node given as nid. The node must be valid and >>>> - * online. For more general interface, see alloc_pages_node(). >>>> - */ >>>> -static inline struct page * >>>> -__alloc_pages_node_noprof(int nid, gfp_t gfp_mask, unsigned int order) >>>> -{ >>>> - VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); >>>> - warn_if_node_offline(nid, gfp_mask); >>>> - >>>> - return __alloc_pages_noprof(gfp_mask, order, nid, NULL); >>>> -} >>>> - >>>> -#define __alloc_pages_node(...) alloc_hooks(__alloc_pages_node_noprof(__VA_ARGS__)) >>>> - >>>> static inline >>>> struct folio *__folio_alloc_node_noprof(gfp_t gfp, unsigned int order, int nid) >>>> { >>>> @@ -293,7 +278,10 @@ static inline struct page *alloc_pages_node_noprof(int nid, gfp_t gfp_mask, >>>> if (nid == NUMA_NO_NODE) >>>> nid = numa_mem_id(); >>>> >>>> - return __alloc_pages_node_noprof(nid, gfp_mask, order); >>>> + VM_BUG_ON(nid < 0 || nid >= MAX_NUMNODES); >>> >>> Could this become a VM_WARN_ON? >> >> Er, it will almost certainly crash later if this is violated. Personally > > You mean in warn_if_node_offline() when accessing the nodemask? > >> if I'm enabling DEBUG_VM I'd rather it crashes with a helpful stacktrace >> instead of chasing random poihnters, likely corrupting memory, and then >> crashing later in a completely undebuggable way instead. > > In this case, VM_WARN_ON + return NULL could work, right? See below. >> >> TBH I don't really understand the "don't BUG" culture we have in Linux. >> I usually just go along with it coz it doesn't seem important enough to >> argue about. But now I'm wondering: if we really don't like VM_BUG_ON() >> why not get rid of it completely? I wonder if there's some case-by-case >> difference that I'm not picking up on. > > My understanding is that issues like the above one should be caught > at development phase, so VM_WARN_ON() is sufficient. > > The source of “don’t BUG”: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1cfd9d7e43d5a1cf739d1420b10b1e65feb02f88 > You can read the commit message to know when BUG_ON() can be used. Quoted from there: I'd prefer to keep all these warnings 'simple' - i.e. no attempted recovery & control flow, unless we ever expect these to trigger. [5] So I wouldn't attempt recovery here. > > Best Regards, > Yan, Zi