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 8283240BCB3; Thu, 11 Jun 2026 16:29:01 +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=1781195342; cv=none; b=bDsqfG2VBSVrWMRmIoD8HI6mpRF26lv84MiscIcZXJ4/RMohfCZPLeKV84FiHW2dNKITvp8ckdJcjjRRE2q6dvzuaVloFMc/4nRY5f6rg+IkWBwjRv0r+k2T9toVd1J55rZCWSqQRjAnYXuv9OQba16e30AfShS5labnU9TQDJY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781195342; c=relaxed/simple; bh=eCHgW1c/bPzmZdQkJm404gAg3fAfJSKPJa2ca3HOz+Y=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=caU0D5jSRHFuAXl51Z0RrSgERVPBBL3HQ/Z3tI8jfG3xyWEhT+qu2IuqHrRQnok1fVyHBY6qJZXssryipuKQA/RaEEJiG6CwqoQrFE022C+INN1BTwxGeKLauF82Sx4tZxMOihAXIhffbrLq6rM6RTI7pIFUFJP8+iBUWNqJk5c= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=jOReuXIR; 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="jOReuXIR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 84F0F1F00893; Thu, 11 Jun 2026 16:28:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1781195341; bh=zFO9PrlKWUdZ371SSeOwADUsueEbVUBHL0tzrlGjCbQ=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=jOReuXIRmEjh18yo6hQMRXe3pzeKqJHWt7xU7PmsWG5/BDmspraKVXqznLoLzzGK8 kYIhBBwoaHRcIvuIzfeUpmvHE2cVgUaxbs235Es3prqRn8SEHcXaYYaX+A/LdpSSqQ 7vVkklTqsBmfbtAUt7m78KWuK/g++bohtCxmcpLwqpP0eLRp6mQMl0SRPl+GoLA4cx ojuVNc8XepIq0+dbLYw4PtirEV1hjWW3bDtv4F/RA1BtlOqgX+7XgZqJowIIce6JJY BekMe54d/ts5wsxHQK5fgeWvXr6YHmSBPd2g7Y6v/zHOGOPudsbkTJpiL0lCeUjcbv cJmOKxN7E9KcQ== Message-ID: Date: Thu, 11 Jun 2026 18:28:55 +0200 Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 15/16] mm/slab: remove __GFP_NO_OBJ_EXT usage from alloc_slab_obj_exts() 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: <20260610-slab_alloc_flags-v2-0-7190909db118@kernel.org> <20260610-slab_alloc_flags-v2-15-7190909db118@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 17:40, Vlastimil Babka (SUSE) wrote: > __GFP_NO_OBJ_EXT has limited scope within the slab allocator itself and > gfp flags are a scarce resource, unlike slab's alloc_flags. > > Introduce SLAB_ALLOC_NO_RECURSE alloc flag that has the same intent as > __GFP_NO_OBJ_EXT but a more generic name, meaning that a kmalloc() > family function should not recurse into another kmalloc*() for the > purposes of allocating auxiliary structures (obj_ext arrays or sheaves). > > First, replace the __GFP_NO_OBJ_EXT for allocating obj_ext arrays in > alloc_slab_obj_exts(). Make use of the newly added kmalloc_flags() > function, where we can pass alloc_flags with SLAB_ALLOC_NO_RECURSE > added. This will also pass through SLAB_ALLOC_TRYLOCK so we don't need > to special case kmalloc_nolock() anymore. > > Note that until now the kmalloc_nolock() ignored the incoming gfp flags > and hardcoded __GFP_ZERO | __GFP_NO_OBJ_EXT. But it's correct to pass on > the incoming gfp flags (only augmented with __GFP_ZERO), because if > alloc_flags contain SLAB_ALLOC_TRYLOCK, the incoming gfp flags have to > be also compatible with it. > > Signed-off-by: Vlastimil Babka (SUSE) As pointed out by Sashiko, this piecemeal approach creates a bisection hazard where sheaves -> obj_ext -> sheaves -> ... recursion can happen. So I'll changes this as follows to make obj_ext accept and pass both the gfp and alloc_flags preventing recursion, and change the next patch to revert that temporary change again. diff --git a/mm/slub.c b/mm/slub.c index a81f1f6bad67..c60f3a252ae5 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2167,6 +2167,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, gfp &= ~OBJCGS_CLEAR_MASK; /* Prevent recursive extension vector allocation */ + gfp |= __GFP_NO_OBJ_EXT; alloc_flags |= SLAB_ALLOC_NO_RECURSE; sz = obj_exts_alloc_size(s, slab, gfp); @@ -2371,7 +2372,7 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags, if (s->flags & (SLAB_NO_OBJ_EXT | SLAB_NOLEAKTRACE)) return; - if (alloc_flags & SLAB_ALLOC_NO_RECURSE) + if (alloc_flags & SLAB_ALLOC_NO_RECURSE || flags & __GFP_NO_OBJ_EXT) return; slab = virt_to_slab(object);