logfs: query block device for number of pages to send with bio (9f0bbd8c) · Commits · 戴 / test

The block device driver puts a limit on maximum number of pages that can be sent with the bio. Not all block devices can handle BIO_MAX_PAGES number of pages in bio. Specifically the virtio-blk diriver limits it to 126. When the LogFS file system was excersized in KVM, the following bug from do_virtblk_request() was observed static void do_virtblk_request(struct request_queue *q) { .... .... while ((req = blk_peek_request(q)) != NULL) { BUG_ON(req->nr_phys_segments + 2 > vblk->sg_elems); .... .... } .... } The patch fixes the problem by querring the maximum number of pages in bio allowed from block device driver and then using those many pages during submit_bio. Signed-off-by:

Prasad Joshi <prasadjoshi.linux@gmail.com>

fs/logfs/dev_bdev.c

+6 −8

Original line number	Diff line number	Diff line
		@@ -96,12 +96,11 @@ static int __bdev_writeseg(struct super_block *sb, u64 ofs, pgoff_t index,
		struct address_space *mapping = super->s_mapping_inode->i_mapping;
		struct bio *bio;
		struct page *page;
		struct request_queue *q = bdev_get_queue(sb->s_bdev);
		unsigned int max_pages = queue_max_hw_sectors(q) >> (PAGE_SHIFT - 9);
		unsigned int max_pages;
		int i;

		if (max_pages > BIO_MAX_PAGES)
		max_pages = BIO_MAX_PAGES;
		max_pages = min(nr_pages, (size_t) bio_get_nr_vecs(super->s_bdev));

		bio = bio_alloc(GFP_NOFS, max_pages);
		BUG_ON(!bio);

		@@ -191,12 +190,11 @@ static int do_erase(struct super_block *sb, u64 ofs, pgoff_t index,
		{
		struct logfs_super *super = logfs_super(sb);
		struct bio *bio;
		struct request_queue *q = bdev_get_queue(sb->s_bdev);
		unsigned int max_pages = queue_max_hw_sectors(q) >> (PAGE_SHIFT - 9);
		unsigned int max_pages;
		int i;

		if (max_pages > BIO_MAX_PAGES)
		max_pages = BIO_MAX_PAGES;
		max_pages = min(nr_pages, (size_t) bio_get_nr_vecs(super->s_bdev));

		bio = bio_alloc(GFP_NOFS, max_pages);
		BUG_ON(!bio);

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