From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-180.mta1.migadu.com (out-180.mta1.migadu.com [95.215.58.180]) (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 58916416CE8 for ; Tue, 9 Jun 2026 13:35:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.180 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781012158; cv=none; b=OaYLcwuuBBmBieilFqSRL6j8/spKkQ2CARSCIKmgXvFmmS59GY2bMYfOro4gsbETInI/3olwQDtuQ6Zob5k2lJ5nwO8iljkkoIHJnDtj1vBRT4OJaUqApyGWrvfYvEOvAVEzDA7bYxc7nZnqE6lPqyehsPTy26AczQV819lh324= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781012158; c=relaxed/simple; bh=8BiK1KxFqztyD5pyllvGHSu2mNRsxr7nrC6FMk+3mWM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=s9euku5SlZB0WakoScv6lqLHfOsyF3J6aQIR1a0sruKYedAK7iXTb6u0o5ZII3a4Lf8S4zyAoif8Dfk63aKsV6/N0rn5jIskSj4plSYYclxfjnF1s3HOp+Hz/9TtBIkxBvcqK23bYXnISyXLWikbTingzYxkz763/afEhnwZO+c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev; spf=pass smtp.mailfrom=linux.dev; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b=QzMh49Ds; arc=none smtp.client-ip=95.215.58.180 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.dev Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.dev Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.dev header.i=@linux.dev header.b="QzMh49Ds" X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1781012144; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=Fac/qHX5WhfF08NyL9azVrutmt3ga+s6RNOocK4YyzE=; b=QzMh49DsK+rj/HXv5ZB23N3Vey836AfUWpRWeQB+4uJpkIFKUHr/nYKDkrrc3u9axP/w6+ G8LnrLfGwv5PmvjS5plSoaMlSixod6mR3J7+nv+mIwdPz2OS4IGGsXKprqsCyP4tQInw82 IWHwXtMn288yweMaFWfxY47HQQDv6/g= From: Usama Arif To: "Vlastimil Babka (SUSE)" Cc: Usama Arif , Harry Yoo , hao.ge@linux.dev, 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 Subject: Re: [PATCH RFC 00/15] mm/slab: introduce alloc_flags and slab_alloc_context Date: Tue, 9 Jun 2026 06:35:33 -0700 Message-ID: <20260609133534.3548059-1-usama.arif@linux.dev> In-Reply-To: <20260609-slab_alloc_flags-v1-0-2bf4a4b9b526@kernel.org> References: Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT On Tue, 09 Jun 2026 11:17:45 +0200 "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. > Hello Valstimil! I think memory allocation profiling uses __GFP_NO_OBJ_EXT, and I dont see it being removed in the series (hopefully I didnt miss it). Adding Hao Ge in CC who did this in the commit: mm/alloc_tag: replace fixed-size early PFN array with dynamic linked list > 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; > }; > > 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) > >