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 AC1A4318BB3 for ; Thu, 28 May 2026 07:26:16 +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=1779953177; cv=none; b=ALQPBQSuLra9eDYs1A5mKmQeSJLg6+RPwmW7b9HYJm1rjwMpWyZtL9e/O7Y8N34ncyhzCGg4q0M0bQyO88CF10owPykzb51yjxmUDVNKiCXxLuYIfTNxdKqXoixTKRz5ANY80NVTAaVKvqrJ1IWgENQypfCRpY3iU7XfTTgtloc= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779953177; c=relaxed/simple; bh=M6qhGnw3PBu7OTg551h4TuTaslLSmhrSkl1qTNLqrkg=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=WjA9oB23tRzcc+FNrVDDH3aOhJgFvidc6aQ1ejPpgpnL/CB4p6ixCJYIIM9auRto8rFGQ2kWGA+vzvvtyeutYwBTKly7Vb7FsqbZFAgMNrxpQen1AGNuvvFWPlpJGu/Vgb/GQ79EH1GRisPGVhE6mazlnO4triWkvACpaRRaMDo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZIRv59Ei; 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="ZIRv59Ei" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1CB211F000E9; Thu, 28 May 2026 07:26:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1779953176; bh=DpIXayEEnCYbKVNRKoSQmDaY/1iplluWjMjEmB3ZBdo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZIRv59Ein6LfaRCNIS9eZRglbpA89knsGFBp+GnEIwosaFypVVQQ2WzLcHicB/sTi 7lTEJTsr+kD1WnsCHWl1Mph3kUW/GxpCleUcw4VHIbcV74BuE2otCZe2z0y76h+f8q GIVppho07XsCNCplmnQCZKV+s3U/PD1La7ggSEtV1eoXAezWYUmebvdzZXBwTG929v g5ActMPukCdQ20+IUuouPaz9xrjuk7nsy5leR7Dmnk848MjfXJCrQeJVyuBXKJPcGU kudbwBIIqTBE8BCigNW79mOEPc9andUQjc3ikK2/+U/cO7TkZI6BQz05hhmaMLLQ9i jlrxP5E0yOPVA== Message-ID: <8d65937a-f2c1-498e-9272-d80ae6649285@kernel.org> Date: Thu, 28 May 2026 09:26:11 +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 v4] mm/slub: use empty sheaf helpers for oversized sheaves Content-Language: en-US To: hu.shengming@zte.com.cn Cc: surenb@google.com, harry@kernel.org, akpm@linux-foundation.org, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, zhang.run@zte.com.cn, cai.qu@zte.com.cn References: <20260528143733563XhbDWw9ZGOiFU9KHd72Xu@zte.com.cn> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 5/28/26 08:37, hu.shengming@zte.com.cn wrote: > VlastimilBabka(SUSE) wrote: >>On 5/27/26 15:48, hu.shengming@zte.com.cn wrote: >> >> I see, thanks. Could we perhaps move the mark_obj_codetag_empty() code to >> alloc_empty_sheaf()? If not, then do as you suggest? >> > > I looked at moving mark_obj_codetag_empty() to alloc_empty_sheaf(), but I > don't think it is equivalent to doing it on the free path. > > mark_obj_codetag_empty() only marks an entry if the slab already has > slabobj_exts. For sheaf metadata allocated with __GFP_NO_OBJ_EXT, the > allocation hook will not create the object extension. So if the slab has > no obj_exts at allocation time, an allocation-time mark would be a no-op. > A slabobj_ext can still be created later for the same kmalloc slab by > another allocation, and then freeing the sheaf without marking it on the > free path can still leave the sheaf entry with a NULL tag. Ah right, makes sense. > So I think the marking should stay in free_empty_sheaf(). I can still > move the caller-GFP filtering out of __alloc_empty_sheaf(). That includes > both clearing OBJCGS_CLEAR_MASK and handling the early rejection of > caller-supplied __GFP_NO_OBJ_EXT: > > if (gfp & __GFP_NO_OBJ_EXT) > return NULL; > > Moving this filtering to the caller would let the oversized prefill path > avoid losing __GFP_NOFAIL.But I would keep the SLAB_KMALLOC-specific > __GFP_NO_OBJ_EXT allocation and the matching free-time mark together. Sounds good! Thanks! > Please let me know if you have a better suggestion. > > -- > With Best Regards, > Shengming