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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: Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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