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 29E2C33CEA8; Wed, 10 Jun 2026 14:04:21 +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=1781100263; cv=none; b=bVtdsRXfRM0M2FdpFQjUhVH7nCmS24qHhSgx4amxuew8o19DgedHiepzRTyVCGagFdWjZgvM/m9fPau0ySgCtAtP+4pw/OWrh+sg8qXcmgYr/xl8tvLQ6Ubxywqwiv5Sl926xMeukTG/WGhB10KwTqIhhfbkXWwK5Uf2iXljeo8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781100263; c=relaxed/simple; bh=ZAgIGcFyTgo8OZNINn6R1wPxSuL5Cv9V5+N3MRgOtMQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=GG5qT8adHXhHpnDtNwLVep7jfcm23zIRr/TLT2iollOGVzXp22Adz9C8d8ZiYd44fYaF8K4Htgqd2sAOVlXz/Syi7fznGPY2FZFt/uGSFDyZr2JceauocPbhhYbQJHj0qFbLDTLJZ+Y++yH0lhP4Tlg+I/ThBmhgVEnxVkAMMAU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IZ27F55V; 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="IZ27F55V" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6ABCA1F00893; Wed, 10 Jun 2026 14:04:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781100261; bh=9WoSNkxkAmlgrYK5pk3MND8Naa2H15fz8ABwUK5IjXY=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=IZ27F55VADckRYY8xgm9G5m7RFOh2m9iXBN76hocpR5kABCo/Zw5kokS0S0fDpLQ0 KJgYVhRktms9A04Hk8JU+nckrcqwjF6KJ48y6aVWsnm1d4uZQAZySgDlcnks8S2BWW 6p5JD5TN71HgBEjB+R+DtiwcRKSuQItBNxwQ39BzIxjca54eGqrzJezOV/29By0atf LqcA+37V9reCSYLZtZAoba7+Xh37l8cs6/DsqkviPtq9mCoxSSUW/WH5FpgvqUKLTy yX2oOVDSjX8LKFuerQvVIa4B2SHx8gqYv9blvJFStIapgiVRDTZM0PCq5YBldO9/gc N/mUHucPZyDtQ== Message-ID: <0b9dce0f-f2a8-4b52-9c06-600eb13d4a7c@kernel.org> Date: Wed, 10 Jun 2026 16:04:16 +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 RFC 00/15] mm/slab: introduce alloc_flags and slab_alloc_context Content-Language: en-US To: Harry Yoo Cc: Hao Li , Christoph Lameter , David Rientjes , Roman Gushchin , Suren Baghdasaryan , Alexei Starovoitov , Andrew Morton , Johannes Weiner , Michal Hocko , Shakeel Butt , Alexander Potapenko , Marco Elver , Dmitry Vyukov , kasan-dev@googlegroups.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <20260609-slab_alloc_flags-v1-0-2bf4a4b9b526@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 6/10/26 15:46, Harry Yoo wrote: > > > On 6/9/26 6:17 PM, Vlastimil Babka (SUSE) wrote: >> This series is based on slab/for-next. If all goes well, it would >> hopefully go to slab/for-next soon after the 7.2 merge window, so any >> other work can be based on it to avoid conflicts, as it touches a lot >> parts of slab. >> >> Git: https://git.kernel.org/pub/scm/linux/kernel/git/vbabka/linux.git/log/?h=b4/slab_alloc_flags >> >> The slab implementation currently relies on gfp flags to convey >> some context information internally: >> >> - The absence of both __GFP_RECLAIM flags is interpreted as "cannot spin >> on locks", and intended to be used by kmalloc_nolock(). But false >> positives are possible e.g. during early boot where gfp_allowed_mask >> clears __GFP_RECLAIM from all allocations. This leads to unnecessary >> allocation failures and workarounds such as fd3634312a04 ("debugobject: >> Make it work with deferred page initialization - again"). >> >> - __GFP_NO_OBJ_EXT exists and takes up valuable bit in the gfp flags >> space, only to prevent recursive kmalloc() allocations for obj_ext >> arrays and sheaves. > > [ Cc'ing Vishal and Matthew as it's somewhat relevant to memdescs... ] > > When the page allocator starts allocateing slab objects, > we still need a way to avoid recursion for obj_ext arrays and sheaves > (by passing SLAB_ALLOC_NO_RECURSE). > > Looking at kmalloc_flags(), probably we'll end up introducing a separate > gfp type for slab-specific flags? What do you mean by separate gfp type? > Hmm but SLAB_ALLOC_* flags are defined in mm/slab.h and kmalloc_flags() > is defined in include/linux/slab.h. Do yo intend to restrict the slab > alloc flags to MM only? Yeah I don't expect users outside MM. If a valid one appears, we can move it. I should try moving kmalloc_flags() to mm/slab.h as well, unless there's some header dependency issue that will prevent it. >> The page allocator uses its internal alloc_flags to convey various >> context information, including ALLOC_TRYLOCK (meaning "cannot spin"). >> This series copies that concept for the slab allocator, with its own >> slab-specific internal flags: >> >> - SLAB_ALLOC_DEFAULT - no extra flags (the value is 0), but explicit >> - SLAB_ALLOC_TRYLOCK - do not spin on locks (used by kmalloc_nolock()) >> - SLAB_ALLOC_NEW_SLAB - replacing existing 'bool new_slab' parameter >> for allocating obj_ext arrays >> - SLAB_ALLOC_NO_RECURSE - replacing usage of __GFP_NO_OBJ_EXT >> >> To reduce the amount of parameters in various internal functions, we >> additionally introduce slab_alloc_context (also inspired by page >> allocator's alloc_context) for passing a number of existing arguments >> and the new alloc_flags: >> >> /* Structure holding extra parameters for slab allocations */ >> struct slab_alloc_context { >> unsigned long caller_addr; >> unsigned long orig_size; >> unsigned int alloc_flags; >> struct list_lru *lru; >> }; > > Perhaps beyond the scope of the patchset, but I wonder if we could have > something like struct slab_alloc_context but for kmalloc callers to > simplify {PASS,DECL}_KMALLOC_PARAMS(). > > Something like: > > struct kmalloc_params { > #ifdef CONFIG_SLAB_BUCKETS > kmem_buckets *b; > #endif > #ifdef CONFIG_KMALLOC_PARTITION_CACHES > kmalloc_token_t token; > #endif > }; > > The idea is to move optional kmalloc parameters (depending on config) > into a single struct, instead of using the macros. > > void *__kmalloc_node(size_t size, gfp_t flags, int node, > unsigned long caller, > struct kmalloc_params params); > > void *kmalloc_node() { > /* ... snip ...*/ > struct kmalloc_params params = KMALLOC_PARAMS(params.b, params.token); > return __kmalloc_node(size, flags, node, _RET_IP_, params); > } > > The compiler should optimize away unused fields based on the config. > > Per System V AMD64 ABI, the compiler will use registers to pass the > struct, as long as the struct size does not exceed 16 bytes. > (Otherwise it will be passed on stack). Hm but does this work on all architectures, and are we doing this somewhere (for structures larger than a native word) already? Also Marco noted earlier that gcc won't optimize away the struct if it becomes zero-sized: https://lore.kernel.org/all/CANpmjNO1aNm3mKphDGWasK_NUfVY8q4K9GCjyREZFqrOu9WLcw@mail.gmail.com/ >> This also replaces the existing struct partial_context. >> >> The last necessary piece is kmalloc_flags() which can take the >> alloc_flags in addition to gfp flags and is intended for the recursive >> allocations of sheaves and obj_ext arrays, so that both >> SLAB_ALLOC_TRYLOCK and SLAB_ALLOC_NO_RECURSE can be communicated. >> Internally it decides between kmalloc_nolock() and normal kmalloc() >> depending SLAB_ALLOC_TRYLOCK. >> >> The rest of the series is gradually expanding the usage of both >> alloc_flags and slab_alloc_context as necessary, with bits of >> refactoring. Then, __GFP_NO_OBJ_EXT is removed completely. >> >> Note that some usage of gfpflags_allow_spinning() relying on absence of >> __GFP_RECLAIM remains outside of slab (and page allocator) in memcg, >> page_owner and stackdepot code. These can thus yield false-positive >> decisions that spinning is not allowed, but should not result in >> important allocations failing anymore. >> >> Signed-off-by: Vlastimil Babka (SUSE) >> --- >> Vlastimil Babka (SUSE) (15): >> mm/slab: always zero only requested size on alloc >> mm/slab: stop inlining __slab_alloc_node() >> mm/slab: introduce slab_alloc_context >> mm/slab: introduce alloc_flags and SLAB_ALLOC_TRYLOCK >> mm/slab: add alloc_flags to slab_alloc_context >> mm/slab: replace struct partial_context with slab_alloc_context >> mm/slab: pass alloc_flags to new slab allocation >> mm/slab: pass alloc_flags through slab_post_alloc_hook() chain >> mm/slab: replace slab_alloc_node() parameters with slab_alloc_context >> mm/slab: allow kmem_cache_alloc_bulk() with any gfp flags >> mm/slab: pass slab_alloc_context to __do_kmalloc_node() >> mm/slab: introduce kmalloc_flags() >> mm/slab: remove __GFP_NO_OBJ_EXT usage from alloc_slab_obj_exts() >> mm/slab: replace __GFP_NO_OBJ_EXT with SLAB_ALLOC_NO_RECURSE for sheaves >> mm: remove the __GFP_NO_OBJ_EXT flag >> >> include/linux/gfp_types.h | 7 - >> include/linux/slab.h | 14 +- >> include/trace/events/mmflags.h | 10 +- >> lib/alloc_tag.c | 2 +- >> mm/kfence/core.c | 6 +- >> mm/memcontrol.c | 5 +- >> mm/slab.h | 16 +- >> mm/slub.c | 423 ++++++++++++++++++++++++---------------- >> tools/include/linux/gfp_types.h | 7 - >> 9 files changed, 288 insertions(+), 202 deletions(-) >> --- >> base-commit: 500b2c9755301742bdbb61249511ac11a4665dae >> change-id: 20260601-slab_alloc_flags-25c782b0c57c >> >> Best regards, >> -- >> Vlastimil Babka (SUSE) >