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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 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 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 35F732000F X-Rspam-User: X-Stat-Signature: p41uzo7cwmdr8j1yujnpmkxoditwzq51 X-HE-Tag: 1781195342-679971 X-HE-Meta: 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 v1cZam5n wd/QoMyzePh8C+CFWl/Yn1DGmSQpa5vpmr0i1DxFqxm6UmwxZH0BAPB8l4Eqx9PULhqjOklSHZ1BCCdjpigUMEA33KHobyuPmkPd/slu+JzaWl1CWvYX2slo0silyNKitIlOlLia7xDzQHUrEY3duKrifNV9pMFDz8Fjz6J8B0iso3NWObkru58AuzRXi0qzaBgNhIOlA+kaf8gjf/axEPQxjIsn42s4IFmsiYM8d5ABuV0abrsYZv3UjwB2/L9yJrPxASa0PjF5FCjEKo8EZSy3Qym5e7/z9x3QIICir8ttrJzvvUaUNZDhBZQUfEgyoq+GuM/oKX3GY3pQ= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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);