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Mon, 10 Feb 2025 16:56:17 +0800 (CST) Message-ID: Date: Mon, 10 Feb 2025 16:56:17 +0800 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V2] mm/cma: using per-CMA locks to improve concurrent allocation performance To: David Hildenbrand , akpm@linux-foundation.org Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, 21cnbao@gmail.com, baolin.wang@linux.alibaba.com, aisheng.dong@nxp.com, liuzixing@hygon.cn References: <1739152566-744-1-git-send-email-yangge1116@126.com> <51514ffd-a1ca-4eb4-90ab-c6871ab92c95@redhat.com> From: Ge Yang In-Reply-To: <51514ffd-a1ca-4eb4-90ab-c6871ab92c95@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-CM-TRANSID:_____wD3P10xv6lna8IjAw--.4182S2 X-Coremail-Antispam: 1Uf129KBjvJXoWxAF1xXF15XF47XFy8Kr1Utrb_yoWrXw15pr W8GFWjyrWkJr13Aw42vw1DWFyF9wn7KFWUKr1Fva4fCasxCr93Ww48t3WY9rW8urZ7WFyI vr1jqasxZ3WUZrJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDUYxBIdaVFxhVjvjDU0xZFpf9x07jYpB-UUUUU= X-Originating-IP: [112.64.138.194] X-CM-SenderInfo: 51dqwwjhrrila6rslhhfrp/1tbifgbvG2epu8cumgAAsK X-Rspam-User: X-Rspamd-Queue-Id: 112E6C0006 X-Stat-Signature: 66rjh3gt547fcft55uwd73jcafkbfz96 X-Rspamd-Server: rspam03 X-HE-Tag: 1739177783-467547 X-HE-Meta: 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 DPmIGRwF yIO2IPfsJGUQCBAvsXEJ/RV6g0iVh7pZ3E5UCeQqOMFM6z7tz/EqyTiPVzQGkEUlPh9Gc4YPCweE4SQtVQkDrgLSlVXhFVbA74qhsRNSvn/89dp0cfxD4bMCzuv94w4XMQEq4OKwI/YmSV0OOL6+C8BTSezd9R7foLAxMr2tvvk5r3Q38Iw9rVp+/tnCm70vBF5R1DEAJvLsIOOTVDvVagmiXPpfY1qiPln2Dtu0dUzp3AYHL/V8RuZVRk/GZIwN4kMsVXVp7e2n4MlWR1dCe7RXd7zAJarwfYtIKYRTc9JQ6lHZCn9R6ZJWUVcDK84tm/A/gJWUXUPBGs+JHiG+BfaeBYABKzPIYjObFtavZuFfZuIJaR3EOLr3e7sZzpngbDjgNCEmleMoO8m5M1dHAPrrYpoMY/UM18kBR X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 在 2025/2/10 16:34, David Hildenbrand 写道: > On 10.02.25 02:56, yangge1116@126.com wrote: >> From: yangge >> >> For different CMAs, concurrent allocation of CMA memory ideally should >> not >> require synchronization using locks. Currently, a global cma_mutex >> lock is >> employed to synchronize all CMA allocations, which can impact the >> performance of concurrent allocations across different CMAs. >> >> To test the performance impact, follow these steps: >> 1. Boot the kernel with the command line argument hugetlb_cma=30G to >>     allocate a 30GB CMA area specifically for huge page allocations. >> (note: >>     on my machine, which has 3 nodes, each node is initialized with >> 10G of >>     CMA) >> 2. Use the dd command with parameters if=/dev/zero of=/dev/shm/file bs=1G >>     count=30 to fully utilize the CMA area by writing zeroes to a file in >>     /dev/shm. >> 3. Open three terminals and execute the following commands >> simultaneously: >>     (Note: Each of these commands attempts to allocate 10GB [2621440 * >> 4KB >>     pages] of CMA memory.) >>     On Terminal 1: time echo 2621440 > /sys/kernel/debug/cma/hugetlb1/ >> alloc >>     On Terminal 2: time echo 2621440 > /sys/kernel/debug/cma/hugetlb2/ >> alloc >>     On Terminal 3: time echo 2621440 > /sys/kernel/debug/cma/hugetlb3/ >> alloc >> > > Hi, > > I'm curious, what is the real workload you are trying to optimize for? I > assume this example here is just to have some measurement. > Some of our drivers require this optimization, but they haven't been merged into the mainline yet. Therefore, we optimize the debug code for them. > Is concurrency within a single CMA area also a problem for your use case? > Yes, we will first optimize the concurrent performance for multiple CMAs, and then proceed to optimize the concurrent performance for a single CMA later. > >> We attempt to allocate pages through the CMA debug interface and use the >> time command to measure the duration of each allocation. >> Performance comparison: >>               Without this patch      With this patch >> Terminal1        ~7s                     ~7s >> Terminal2       ~14s                     ~8s >> Terminal3       ~21s                     ~7s >> >> To slove problem above, we could use per-CMA locks to improve concurrent >> allocation performance. This would allow each CMA to be managed >> independently, reducing the need for a global lock and thus improving >> scalability and performance. >> >> Signed-off-by: yangge >> --- >> >> V2: >> - update code and message suggested by Barry. >> >>   mm/cma.c | 7 ++++--- >>   mm/cma.h | 1 + >>   2 files changed, 5 insertions(+), 3 deletions(-) >> >> diff --git a/mm/cma.c b/mm/cma.c >> index 34a4df2..a0d4d2f 100644 >> --- a/mm/cma.c >> +++ b/mm/cma.c >> @@ -34,7 +34,6 @@ >>   struct cma cma_areas[MAX_CMA_AREAS]; >>   unsigned int cma_area_count; >> -static DEFINE_MUTEX(cma_mutex); >>   static int __init __cma_declare_contiguous_nid(phys_addr_t base, >>               phys_addr_t size, phys_addr_t limit, >> @@ -175,6 +174,8 @@ static void __init cma_activate_area(struct cma *cma) >>       spin_lock_init(&cma->lock); >> +    mutex_init(&cma->alloc_mutex); >> + >>   #ifdef CONFIG_CMA_DEBUGFS >>       INIT_HLIST_HEAD(&cma->mem_head); >>       spin_lock_init(&cma->mem_head_lock); >> @@ -813,9 +814,9 @@ static int cma_range_alloc(struct cma *cma, struct >> cma_memrange *cmr, >>           spin_unlock_irq(&cma->lock); >>           pfn = cmr->base_pfn + (bitmap_no << cma->order_per_bit); >> -        mutex_lock(&cma_mutex); >> +        mutex_lock(&cma->alloc_mutex); >>           ret = alloc_contig_range(pfn, pfn + count, MIGRATE_CMA, gfp); >> -        mutex_unlock(&cma_mutex); >> +        mutex_unlock(&cma->alloc_mutex); > > > As raised, a better approach might be to return -EAGAIN  in case we hit > an isolated pageblock and deal with that more gracefully here (e.g., try > another block, or retry this one if there are not others left, ...) > > In any case, this change here looks like an improvement. > > Acked-by: David Hildenbrand >