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Wed, 29 Mar 2023 00:33:11 -0400 X-MC-Unique: 9eGy4BwpN02NIhmiOtAIWw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 1A2AE80C8C2; Wed, 29 Mar 2023 04:33:11 +0000 (UTC) Received: from localhost (ovpn-12-137.pek2.redhat.com [10.72.12.137]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 2B428C15BA0; Wed, 29 Mar 2023 04:33:09 +0000 (UTC) Date: Wed, 29 Mar 2023 12:33:05 +0800 From: Baoquan He To: Uladzislau Rezki Cc: Andrew Morton , linux-mm@kvack.org, LKML , Lorenzo Stoakes , Christoph Hellwig , Matthew Wilcox , Dave Chinner , Oleksiy Avramchenko Subject: Re: [PATCH v3 1/2] mm: vmalloc: Remove a global vmap_blocks xarray Message-ID: References: <20230327170126.406044-1-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 7F3574000E X-Stat-Signature: tfqkciu4hbh6pzop4xj67pzqyiggrrqt X-HE-Tag: 1680064397-98089 X-HE-Meta: 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 8pPi4Vwj OBhE7Gv9ikUzVCvwlx2v7ZKRfXOiRXndu+TLIRYdVnzZurlkW+G61Smeqvwag4vz0cq6cX58cl3LXa7uuWb4uIEPYq6PuZTBLAGLLkAcKJ+PU+t8l6upBQ0u+rvgdUMzsKkOelPB0oy1NrISVDKe6vezycfmagh+RdLxgB5h4lzK/VyXMiaZdqnQXx5Ahc6YSHctl9Nzy5h9XTAX6p4i81Zb3TTQ3Nn2e5QUYiRYaZuHk5V+PoEpnJgJkkH51UoLwff2p8Ja37KAL6yg= 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 03/28/23 at 02:34pm, Uladzislau Rezki wrote: ...... > > > @@ -2003,8 +2037,8 @@ static void *new_vmap_block(unsigned int order, gfp_t gfp_mask) > > > bitmap_set(vb->used_map, 0, (1UL << order)); > > > INIT_LIST_HEAD(&vb->free_list); > > > > > > - vb_idx = addr_to_vb_idx(va->va_start); > > > - err = xa_insert(&vmap_blocks, vb_idx, vb, gfp_mask); > > > + vbq = addr_to_vbq(va->va_start); > > > + err = xa_insert(&vbq->vmap_blocks, va->va_start, vb, gfp_mask); > > > > Using va->va_start as index to access xarray may cost extra memory. > > Imagine we got a virtual address at VMALLOC_START, its region is > > [VMALLOC_START, VMALLOC_START+4095]. In the xarray, its sequence order > > is 0. While with va->va_start, it's 0xffffc90000000000UL on x86_64 with > > level4 paging mode. That means for the first page size vmalloc area, > > storing it into xarray need about 10 levels of xa_node, just for the one > > page size. With the old addr_to_vb_idx(), its index is 0. Only one level > > height is needed. One xa_node is about 72bytes, it could take more time > > and memory to access va->va_start. Not sure if my understanding is correct. > > > > static unsigned long addr_to_vb_idx(unsigned long addr) > > { > > addr -= VMALLOC_START & ~(VMAP_BLOCK_SIZE-1); > > addr /= VMAP_BLOCK_SIZE; > > return addr; > > } > > > If the size of array depends on index "length", then, indeed it will require > more memory. From the other hand we can keep the old addr_to_vb_idx() function > in order to "cut" a va->va_start index. Yeah, the extra 10 levels of xa_node is unnecessary if we keep the old addr_to_vb_idx(). And the prolonged path will cost more time to reach the wanted leaf node. E.g on x86_64 with 4 level paging mode, vmalloc area is 32TB. With the old calculation, its index range is [0, 8M], 4 level heights of xa_node at most is enough to cover.