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 998D8431E67; Thu, 16 Jul 2026 14:43:42 +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=1784213029; cv=none; b=o1P51w3PX2EFCysedJYXsEgd3BMauwQdyEiaOmE/CgekVdHWat6R0dZSi8fkVJKLwB8RlvPqpejVabvehrVnqZCIC2wLtOCak7PrHybeRlvPXYvSfFBgItquIFnBk4ue+JsPJGu6lsW9UeE/HoWJE99/AZf8n7bRjRFmQZ3Uhic= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1784213029; c=relaxed/simple; bh=mTe8D8nzgtbigkSBp1hbXfnITsUxOIHKOJYVryZbmRo=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=uCtF6pqYUkbX+kWRKlPSTZ15mvypY6ofX5mmTXxO0pvvbGP5ov9J6TSDPQuSX47a4R6fJIBNKLBRNFdnqS5RvfXmNccTt4L6J6PuWAmpd1emtD7RBgt5vnBuaT7Y5UdVvVV3/cWrJF/7BsB8wFX+X3vNQ9fGWp7uovrZqPDLJKI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FJauAJak; 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="FJauAJak" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A6C0C1F000E9; Thu, 16 Jul 2026 14:43:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1784213020; bh=mU+AkHG+unovjoou+Gc++cD5SyJh4xwusPC7zchS0m8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FJauAJakhRvLtd584lr/GAriHLfmUjBqPUdRIv4YrgWA5IhTqvb2tRcX1o3i24R+g 2broTkPr1VeFpwXQXpsesKck8xUKjn83EjzPBr+yqgR86w4zBP2aCYT00Cyd2D2cix MPeXf+WXorOO0Rj40ZtpBDXH2RA/12A1xbXD7FbhFEUpMG5hgiCDiPukBTEedWe6UH 9hPL/878X3Rs4xlvQjToaIItSVqWLW2hOQ6RBfrZ3UtIibFGKvR8bhvbGRZyEKSLnU u9w+91zOogOw1vMlsvBhVj2vSKayZKuflTHagKlETCzG+3EdoJU4Mn4mixnFkK5pPV lqcN8AinTwW6g== Message-ID: <01aa6803-e6a7-4172-94ef-043914e2f794@kernel.org> Date: Thu, 16 Jul 2026 16:43:36 +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 RFC 08/12] mm/slab: change struct slabobj_ext to a union Content-Language: en-US To: Suren Baghdasaryan Cc: Harry Yoo , Hao Li , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <20260715-b4-objext_split-v1-0-9a49c4ccf4c3@kernel.org> <20260715-b4-objext_split-v1-8-9a49c4ccf4c3@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 8bit On 7/16/26 06:11, Suren Baghdasaryan wrote: > On Wed, Jul 15, 2026 at 3:11 AM Vlastimil Babka (SUSE) > wrote: >> No functional change intended, the layout is still effectively static. >> >> Signed-off-by: Vlastimil Babka (SUSE) > > This is much cleaner than what I was preparing. Nicely done! > > Reviewed-by: Suren Baghdasaryan Thanks! >> --- >> mm/slab.h | 41 +++++++++++++++++++++++++++++++++-------- >> mm/slub.c | 17 +++++++++-------- >> 2 files changed, 42 insertions(+), 16 deletions(-) >> >> diff --git a/mm/slab.h b/mm/slab.h >> index 3ad9777ad600..359ab8caf61e 100644 >> --- a/mm/slab.h >> +++ b/mm/slab.h >> @@ -554,14 +554,34 @@ static inline bool need_kmalloc_no_objext(void) >> * if MEMCG_DATA_OBJEXTS is set. >> */ >> struct slabobj_ext { > > Perhaps we should add a comment here stating that every element of > this union should be pointer-sized? > OK, how about this? --- a/mm/slab.h +++ b/mm/slab.h @@ -550,10 +550,14 @@ static inline bool need_kmalloc_no_objext(void) } /* - * Extended information for slab objects stored as an array in page->memcg_data - * if MEMCG_DATA_OBJEXTS is set. + * Extended information for slab objects stored as a pointer to an array in + * slab->obj_exts (aliasing page->memcg_data) if MEMCG_DATA_OBJEXTS is set. */ struct slabobj_ext { + /* + * All elements of the union should be pointer-sized to avoid memory + * waste + */ union { #ifdef CONFIG_MEMCG struct obj_cgroup *_objcg;