From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from out-179.mta1.migadu.com (out-179.mta1.migadu.com [95.215.58.179]) (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 512B824BBFD for ; Thu, 21 May 2026 01:01:55 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=95.215.58.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779325317; cv=none; b=azPkBBNP++9yq2u9vQHInE2W3afZ4PDBdssCkz3wSndVDyJDDFU7bEa7s/wGhugR4XgyrX2sJrtjBlKB6ac+El8wCocEVeH80NFwKpHVpdQVDmTgR9yveSBw04RFeXUQSI1B8dDsZQ8HfOulusQXOTR98mGLziCSVywitHYChf8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1779325317; c=relaxed/simple; bh=1nOSyPNSmCQ/i7zE+Zk8FkfLP4yEaJjqcXtopu96evA=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=nlZrCwNShyDjFFjt2GMl2iWV1j13fb2b2WcNA+vqoRPt+OHeCIBP0o2JAPwnmvXNctFdl3NtdE1tnbQvj/aTvHiNCiz/mpKs34nvXWcJIc/gpEqruCXJzKLBOYowpI084tmCc4prr0DZO975VzeD5QrPCXCmA7z06ZuVf/HlyXk= 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=LE8g0B/v; arc=none smtp.client-ip=95.215.58.179 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="LE8g0B/v" Date: Wed, 20 May 2026 18:01:30 -0700 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779325303; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=N6+eCAO9BUhXRuKgK/q3rPe94yeakgzBDRKqgv0P63E=; b=LE8g0B/vDcnIlCW6Tn+CdVICwGSpp0kHWRyiIVzSfJQxgHaUVCsj+vP7wxYFU0CeHTovPV ueE2l0yfH5UUOw9Rchqd8mw6i5zjC7QrXobCW2RrPImRrwnzf9B0blMA5ZH95XQWs9mPnL 6x2ORFtbESwq8Jv717LlEr5fepfUea8= X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Shakeel Butt To: Harry Yoo Cc: Andrew Morton , Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Alexandre Ghiti , Joshua Hahn , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot Subject: Re: [PATCH 2/4] memcg: uint16_t for nr_bytes in obj_stock_pcp Message-ID: References: <20260520053123.2709959-1-shakeel.butt@linux.dev> <20260520053123.2709959-3-shakeel.butt@linux.dev> <55d36f91-fcae-4506-9b76-4a7cad3d256d@kernel.org> Precedence: bulk X-Mailing-List: cgroups@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <55d36f91-fcae-4506-9b76-4a7cad3d256d@kernel.org> X-Migadu-Flow: FLOW_OUT On Wed, May 20, 2026 at 04:01:45PM +0900, Harry Yoo wrote: > > > On 5/20/26 2:31 PM, Shakeel Butt wrote: > > Currently struct obj_stock_pcp stores nr_bytes in an 'unsigned int' > > which is 4 bytes on 64-bit machines. Switch the field to uint16_t to > > shrink the per-CPU cache. > > > > The kernel supports PAGE_SIZE_4KB, _8KB, _16KB, _32KB, _64KB and > > _256KB (see HAVE_PAGE_SIZE_* in arch/Kconfig). After the > > PAGE_SIZE-aligned flush in __refill_obj_stock(), the sub-page > > remainder fits in uint16_t up through 64KiB pages where PAGE_SIZE - 1 > > == U16_MAX, but on 256KiB pages PAGE_SIZE - 1 == 0x3FFFF exceeds > > U16_MAX. The accumulator also needs to stay within uint16_t between > > page-aligned flushes on 64KiB pages where PAGE_SIZE itself is > > U16_MAX + 1. > > > > Accumulate the new total in an 'unsigned int' local, then: > > > > 1. Flush whenever the accumulator would hit U16_MAX. Together with > > the existing allow_uncharge flush at PAGE_SIZE, this keeps the > > uint16_t safe on PAGE_SIZE <= 64KiB. > > > > 2. On configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on hexagon and > > powerpc 44x), push any sub-page remainder above U16_MAX into > > objcg->nr_charged_bytes via atomic_add before storing back, so > > the store cannot silently truncate. The PAGE_SHIFT > 16 guard > > folds the branch out at compile time on smaller page sizes. > > > > Signed-off-by: Shakeel Butt > > Tested-by: kernel test robot > > --- > > mm/memcontrol.c | 33 +++++++++++++++++++++++++++------ > > 1 file changed, 27 insertions(+), 6 deletions(-) > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > index d7c162946719..b3d63d9f267c 100644 > > --- a/mm/memcontrol.c > > +++ b/mm/memcontrol.c > > @@ -3339,21 +3340,41 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, > > goto out; > > } > > + stock_nr_bytes = stock->nr_bytes; > > if (READ_ONCE(stock->cached_objcg) != objcg) { /* reset if necessary */ > > drain_obj_stock(stock); > > obj_cgroup_get(objcg); > > - stock->nr_bytes = atomic_read(&objcg->nr_charged_bytes) > > + stock_nr_bytes = atomic_read(&objcg->nr_charged_bytes) > > ? atomic_xchg(&objcg->nr_charged_bytes, 0) : 0; > > WRITE_ONCE(stock->cached_objcg, objcg); > > allow_uncharge = true; /* Allow uncharge when objcg changes */ > > } > > - stock->nr_bytes += nr_bytes; > > + stock_nr_bytes += nr_bytes; > > + > > + /* Since stock->nr_bytes is uint16_t, don't refill >= U16_MAX */ > > + if ((allow_uncharge && (stock_nr_bytes > PAGE_SIZE)) || > > + stock_nr_bytes >= U16_MAX) { > > nit: This should be > U16_MAX? Ack.