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[90.233.209.15]) by smtp.gmail.com with ESMTPSA id v21-20020a2e7a15000000b00295b1ad177csm2608383ljc.68.2023.03.22.11.02.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Mar 2023 11:02:02 -0700 (PDT) From: Uladzislau Rezki X-Google-Original-From: Uladzislau Rezki Date: Wed, 22 Mar 2023 19:01:59 +0100 To: Matthew Wilcox Cc: Uladzislau Rezki , Dave Chinner , Lorenzo Stoakes , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton , Baoquan He , David Hildenbrand , Liu Shixin , Jiri Olsa Subject: Re: [PATCH v2 2/4] mm: vmalloc: use rwsem, mutex for vmap_area_lock and vmap_block->lock Message-ID: References: <6c7f1ac0aeb55faaa46a09108d3999e4595870d9.1679209395.git.lstoakes@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 82C3980031 X-Stat-Signature: 8dx1bgkxafmtymqsszwtt3mbro86p8zt X-Rspam-User: X-HE-Tag: 1679508125-576574 X-HE-Meta: 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 P+QDbl5U 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 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: On Wed, Mar 22, 2023 at 05:47:28PM +0000, Matthew Wilcox wrote: > On Wed, Mar 22, 2023 at 02:18:19PM +0100, Uladzislau Rezki wrote: > > Hello, Dave. > > > > > > > > I'm travelling right now, but give me a few days and I'll test this > > > against the XFS workloads that hammer the global vmalloc spin lock > > > really, really badly. XFS can use vm_map_ram and vmalloc really > > > heavily for metadata buffers and hit the global spin lock from every > > > CPU in the system at the same time (i.e. highly concurrent > > > workloads). vmalloc is also heavily used in the hottest path > > > throught the journal where we process and calculate delta changes to > > > several million items every second, again spread across every CPU in > > > the system at the same time. > > > > > > We really need the global spinlock to go away completely, but in the > > > mean time a shared read lock should help a little bit.... > > > > > Could you please share some steps how to run your workloads in order to > > touch vmalloc() code. I would like to have a look at it in more detail > > just for understanding the workloads. > > > > Meanwhile my grep agains xfs shows: > > > > > > urezki@pc638:~/data/raid0/coding/linux-rcu.git/fs/xfs$ grep -rn vmalloc ./ > > You're missing: > > fs/xfs/xfs_buf.c: bp->b_addr = vm_map_ram(bp->b_pages, bp->b_page_count, > > which i suspect is the majority of Dave's workload. That will almost > certainly take the vb_alloc() path. > Then it has nothing to do with vmalloc contention(i mean global KVA allocator), IMHO. Unless: void *vm_map_ram(struct page **pages, unsigned int count, int node) { unsigned long size = (unsigned long)count << PAGE_SHIFT; unsigned long addr; void *mem; if (likely(count <= VMAP_MAX_ALLOC)) { mem = vb_alloc(size, GFP_KERNEL); if (IS_ERR(mem)) return NULL; addr = (unsigned long)mem; } else { struct vmap_area *va; va = alloc_vmap_area(size, PAGE_SIZE, VMALLOC_START, VMALLOC_END, node, GFP_KERNEL); if (IS_ERR(va)) return NULL; number of pages > VMAP_MAX_ALLOC. That is why i have asked about workloads because i would like to understand where a "problem" is. A vm_map_ram() access the global vmap space but it happens when a new vmap block is required and i also think it is not a problem. But who knows, therefore it makes sense to have a lock at workload. -- Uladzislau Rezki