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DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1779766814; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=DhCjAMoSVz9odIihzeNS/7m2ssbSIYp4a1jvAvsbJjI=; b=fEU5/DyU6aWgLcZRzwlOoaHUpbf3wC6CXYF4Nk89wq6qtBtJD7upZ9CgEWEORch3biQASN EK/+xE9Ae6KPnLk45aegdJiNG33fImRIlaTzZbbk24OtpfDivoumCYqjEmQFA6rNYfssCV LXdhdBGcizL2+3BW8PkvPs4ul0k2vYY= From: Shakeel Butt To: Andrew Morton Cc: Johannes Weiner , Michal Hocko , Roman Gushchin , Muchun Song , Qi Zheng , Alexandre Ghiti , Joshua Hahn , Harry Yoo , David Laight , Meta kernel team , linux-mm@kvack.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, kernel test robot Subject: [PATCH v3 2/4] memcg: uint16_t for nr_bytes in obj_stock_pcp Date: Mon, 25 May 2026 20:39:29 -0700 Message-ID: <20260526033931.1760588-3-shakeel.butt@linux.dev> In-Reply-To: <20260526033931.1760588-1-shakeel.butt@linux.dev> References: <20260526033931.1760588-1-shakeel.butt@linux.dev> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT X-Stat-Signature: s8xxao8siaomsroihggnund7e7gxht94 X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: 98D54140010 X-HE-Tag: 1779766815-753607 X-HE-Meta: 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 62NRGozW NA+kBu2oQWCq5L9sWolUh5AMa2DK8wjBQncAoLq/zz/nhS9uzdvlsgWeP1s14gr6YeuvUsCAVyWp7/hQD7kT4V1MH0W+TXwAIpJDSoZiAeacZWLy8JrPCtICq1AgUwwa+uxQS9CsYMUQXTbMPCi8F5r6R5O82cfqYfGJAyBpZtyspQZhJ9XoaEloDgYSImS/SQq9HNPteB7YVxebl3oJnTm2PyrnDQ36L0BRZlrt87llQ4LqT9cbpXXK5D/0G8gaghCRxTGuxjsMROOqjxSuBw+tBVE3SGww7mdXf9/ytgzM++1CTGVZW/5fZ2Tm5ynFQeDBMo5wJ5Vld069nRAGveTdqiG8fdfNJ2YskAYwUN5dOMyI= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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 on PAGE_SHIFT <= 16 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 configs with PAGE_SHIFT > 16 (PAGE_SIZE_256KB on hexagon and powerpc 44x, both 32-bit), uint16_t cannot represent the sub-page remainder. Define obj_stock_bytes_t as 'unsigned int' on those archs so nr_bytes can hold the full remainder and the normal page-boundary flush in __refill_obj_stock() and the page extraction in drain_obj_stock() both work correctly. The single-cache-line layout target only applies to PAGE_SHIFT <= 16; those archs are 32-bit embedded and not the optimization target. Fixes: 01b9da291c49 ("mm: memcontrol: convert objcg to be per-memcg per-node type") Tested-by: kernel test robot Reviewed-by: Harry Yoo (Oracle) Acked-by: Qi Zheng Acked-by: Muchun Song Signed-off-by: Shakeel Butt --- Changes since v2: - Based on Sashiko's concern regarding archs with 256KiB base pages, added special handling for such arch and simplify the code overall. - Updated commit message. - Have kept the review tags as overall code remains same mostly. Changes since v1: - Collected tags - Rearrange fields of obj_stock_pcp (David Laight) - Fix comparison operator (Harry) mm/memcontrol.c | 25 +++++++++++++++++++------ 1 file changed, 19 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 9bee9031171f..8c1b65e6da5d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2020,8 +2020,17 @@ static DEFINE_PER_CPU_ALIGNED(struct memcg_stock_pcp, memcg_stock) = { struct obj_stock_pcp { local_trylock_t lock; - unsigned int nr_bytes; struct obj_cgroup *cached_objcg; +#if PAGE_SHIFT > 16 + /* + * On rare archs with 256KiB base page size (hexagon and powerpc 44x) + * keep nr_bytes to unsigned int as uint16_t cannot represent the full + * sub-page remainder. + */ + unsigned int nr_bytes; +#else + uint16_t nr_bytes; +#endif int16_t node_id; int nr_slab_reclaimable_b; int nr_slab_unreclaimable_b; @@ -3334,6 +3343,7 @@ static void __refill_obj_stock(struct obj_cgroup *objcg, bool allow_uncharge) { unsigned int nr_pages = 0; + unsigned int stock_nr_bytes; if (!stock) { nr_pages = nr_bytes >> PAGE_SHIFT; @@ -3342,21 +3352,24 @@ 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; - if (allow_uncharge && (stock->nr_bytes > PAGE_SIZE)) { - nr_pages = stock->nr_bytes >> PAGE_SHIFT; - stock->nr_bytes &= (PAGE_SIZE - 1); + if ((allow_uncharge && (stock_nr_bytes > PAGE_SIZE)) || + stock_nr_bytes > U16_MAX) { + nr_pages = stock_nr_bytes >> PAGE_SHIFT; + stock_nr_bytes &= (PAGE_SIZE - 1); } + stock->nr_bytes = stock_nr_bytes; out: if (nr_pages) -- 2.53.0-Meta