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Tue, 17 Aug 2021 13:43:57 +0000 (UTC) Received: from dovecot-director2.suse.de ([192.168.254.65]) by imap1.suse-dmz.suse.de with ESMTPSA id cF3qAR29G2FFRQAAGKfGzw (envelope-from ); Tue, 17 Aug 2021 13:43:57 +0000 Subject: Re: [PATCH v2 4/4] btrfs: subpage: pack all subpage bitmaps into a larger bitmap To: Qu Wenruo , linux-btrfs@vger.kernel.org References: <20210817093852.48126-1-wqu@suse.com> <20210817093852.48126-5-wqu@suse.com> From: Nikolay Borisov Message-ID: <9599db38-cff8-fac5-c6db-ec1d53beeed3@suse.com> Date: Tue, 17 Aug 2021 16:43:56 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210817093852.48126-5-wqu@suse.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 17.08.21 г. 12:38, Qu Wenruo wrote: > Currently we use u16 bitmap to make 4k sectorsize work for 64K page > size. > > But this u16 bitmap is not large enough to contain larger page size like > 128K, nor is space efficient for 16K page size. > > To handle both cases, here we pack all subpage bitmaps into a larger > bitmap, now btrfs_subpage::bitmaps[] will be the ultimate bitmap for > subpage usage. > > Each sub-bitmap will has its start bit number recorded in > btrfs_subpage_info::*_start, and its bitmap length will be recorded in > btrfs_subpage_info::bitmap_nr_bits. > > All subpage bitmap operations will be converted from using direct u16 > operations to bitmap operations, with above *_start calculated. > > For 64K page size with 4K sectorsize, this should not cause much > difference. > > While for 16K page size, we will only need 1 unsigned long (u32) to > store all the bitmaps, which saves quite some space. > > Furthermore, this allows us to support larger page size like 128K and > 258K. > > Signed-off-by: Qu Wenruo > +#define GANG_LOOKUP_SIZE 16 > static struct extent_buffer *get_next_extent_buffer( > struct btrfs_fs_info *fs_info, struct page *page, u64 bytenr) > { > - struct extent_buffer *gang[BTRFS_SUBPAGE_BITMAP_SIZE]; > + struct extent_buffer *gang[GANG_LOOKUP_SIZE]; > struct extent_buffer *found = NULL; > u64 page_start = page_offset(page); > - int ret; > - int i; > + u64 cur = page_start; > > ASSERT(in_range(bytenr, page_start, PAGE_SIZE)); > - ASSERT(PAGE_SIZE / fs_info->nodesize <= BTRFS_SUBPAGE_BITMAP_SIZE); > lockdep_assert_held(&fs_info->buffer_lock); > > - ret = radix_tree_gang_lookup(&fs_info->buffer_radix, (void **)gang, > - bytenr >> fs_info->sectorsize_bits, > - PAGE_SIZE / fs_info->nodesize); > - for (i = 0; i < ret; i++) { > - /* Already beyond page end */ > - if (gang[i]->start >= page_start + PAGE_SIZE) > - break; > - /* Found one */ > - if (gang[i]->start >= bytenr) { > - found = gang[i]; > - break; > + while (cur < page_start + PAGE_SIZE) { > + int ret; > + int i; > + > + ret = radix_tree_gang_lookup(&fs_info->buffer_radix, > + (void **)gang, cur >> fs_info->sectorsize_bits, > + min_t(unsigned int, GANG_LOOKUP_SIZE, > + PAGE_SIZE / fs_info->nodesize)); > + if (ret == 0) > + goto out; > + for (i = 0; i < ret; i++) { > + /* Already beyond page end */ > + if (gang[i]->start >= page_start + PAGE_SIZE) nit: this could be rewritten as (in_range(gang[i]->start, page_start, PAGE_SIZE) > + goto out; > + /* Found one */ > + if (gang[i]->start >= bytenr) { > + found = gang[i]; > + goto out; > + } > } > + cur = gang[ret - 1]->start + gang[ret - 1]->len; > } > +out: > return found; > } >