Hi， YanYour comment is insightful. It is about the loop invariant, the condition which
must be satisfied when iovs can be combined into one page vector. The loopinvariant is ensured in function dio_get_pagevlen. Note that dio_get_pagevlen should be called before dio_alloc_pagev, so in dio_alloc_pagev, this loop invariant
has been ensured indirectly. Please see my inline comments. I'll deliver a new patch for the newest kernel, using iov_iter KPIs. Best Regards! 在 2015/9/28 11:17, Yan, Zheng 写道:
Hi, zhucaifeng The patch generally looks good. But I think there is minor flaw, see my comment below. Besides, could you write a patch for the newest kernel (it's easier because there is iov_iter_get_pages() helper). On Fri, Sep 25, 2015 at 11:52 AM, zhucaifeng <zhucaifeng@xxxxxxxxxxxxxxx> wrote:Hi, all When using cephfs, we find that cephfs direct io is very slow. For example, installing Windows 7 takes more than 1 hour on a virtual machine whose disk is a file in cephfs. The cause is that when doing direct io, both ceph_sync_direct_write and ceph_sync_read iterate iov elements one by one, and send one osd_op request for each iov that covers about 4K~8K bytes data. The result is lots of small requests and replies shuttled among the kernel client and OSDs. The fix tries to combine as many iovs as possible into one page vector, and then send one request for this page vector. In this way, small requests and replies are reduced; the OSD can serve a large read/write request one time. We observe that the performance is improved by about 5~15 times, dependent on different application workload. The fix is below. Some change notes are as follows: - function ceph_get_direct_page_vetor and ceph_put_page_vector are moved from net/ceph/pagevec.c to fs/ceph/file.c, and are renamed as dio_grab_pages and dio_free_pagev respectively. - function dio_get_pagevlen and dio_alloc_pagev are newly introduced. dio_get_pagevlen is to calculate the page vector length in bytes from the io vectors. Except for the first and last one, an io vector can be merged into a page vector iff its base and tail are page aligned. for the first vector, only its tail should be page aligned; for the last vector, only its head should be page aligned. dio_alloc_pagev allocates pages for each io vector and put these pages together in one page pointer array. Best Regards! --- /home/linux-3.10.0-229.7.2.el7/fs/ceph/file.c 2015-05-16 09:05:28.000000000 +0800 +++ ./fs/ceph/file.c 2015-09-17 10:43:44.798591846 +0800 @@ -34,6 +34,115 @@ * need to wait for MDS acknowledgement. */ +/* + * Calculate the length sum of direct io vectors that can + * be combined into one page vector. + */ +static int +dio_get_pagevlen(const struct iov_iter *it) +{ + const struct iovec *iov = it->iov; + const struct iovec *iovend = iov + it->nr_segs; + int pagevlen; + + pagevlen = iov->iov_len - it->iov_offset; + /* + * An iov can be page vectored when both the current tail + * and the next base are page aligned. + */ + while (PAGE_ALIGNED((iov->iov_base + iov->iov_len)) && + (++iov < iovend && PAGE_ALIGNED((iov->iov_base)))) { + pagevlen += iov->iov_len; + } + dout("dio_get_pagevlen len = %d\n", pagevlen); + return pagevlen; +} + +/* + * Grab @num_pages from the process vm space. These pages are + * continuous and start from @data. + */ +static int +dio_grab_pages(const void *data, int num_pages, bool write_page, + struct page **pages) +{ + int got = 0; + int rc = 0; + + down_read(¤t->mm->mmap_sem); + while (got < num_pages) { + rc = get_user_pages(current, current->mm, + (unsigned long)data + ((unsigned long)got * PAGE_SIZE), + num_pages - got, write_page, 0, pages + got, NULL); + if (rc < 0) + break; + BUG_ON(rc == 0); + got += rc; + } + up_read(¤t->mm->mmap_sem); + return got; +} + +static void +dio_free_pagev(struct page **pages, int num_pages, bool dirty) +{ + int i; + + for (i = 0; i < num_pages; i++) { + if (dirty) + set_page_dirty_lock(pages[i]); + put_page(pages[i]); + } + kfree(pages); +} + +/* + * Allocate a page vector based on (@it, @pagevlen). + * The return value is the tuple describing a page vector, + * that is (@pages, @pagevlen, @page_align, @num_pages). + */ +static struct page ** +dio_alloc_pagev(const struct iov_iter *it, int pagevlen, bool write_page, + int *page_align, int *num_pages) +{ + const struct iovec *iov = it->iov; + struct page **pages; + int n, m, k, npages; + int align; + int len; + void *data; + + data = iov->iov_base + it->iov_offset; + len = iov->iov_len - it->iov_offset; + align = ((ulong)data) & ~PAGE_MASK; + npages = calc_pages_for((ulong)data, pagevlen); + pages = kmalloc(sizeof(*pages) * npages, GFP_NOFS); + if (!pages) + return ERR_PTR(-ENOMEM); + for (n = 0; n < npages; n += m) { + m = calc_pages_for((ulong)data, len); + if (n + m > npages) + m = npages - n; + k = dio_grab_pages(data, m, write_page, pages + n); + if (k < m) { + n += k; + goto failed; + }if (align + len) is not page aligned, the loop should stop.
by modular arithmetic, align + len == data + len (mod PAGE_SIZE),
data + len is PAGE_ALIGNED, due to while loop in dio_get_pagevlen.
Similar to the avove, here (unsigned long)data, that is io->iov_base,+ + iov++; + data = iov->iov_base;if (unsigned long)data is not page aligned, the loop should stop
is PAGE_ALIGNED ensured in the while loop in dio_get_pagevlen.
Regards Yan, Zheng+ len = iov->iov_len; + } + *num_pages = npages; + *page_align = align; + dout("dio_alloc_pagev: alloc pages pages[0:%d], page align %d\n", + npages, align); + return pages; + +failed: + dio_free_pagev(pages, n, false); + return ERR_PTR(-ENOMEM); +} /* * Prepare an open request. Preallocate ceph_cap to avoid an @@ -354,13 +463,14 @@ more: if (ret >= 0) { int didpages; if (was_short && (pos + ret < inode->i_size)) { - u64 tmp = min(this_len - ret, + u64 zlen = min(this_len - ret, inode->i_size - pos - ret); + int zoff = (o_direct ? buf_align : io_align) + + read + ret; dout(" zero gap %llu to %llu\n", - pos + ret, pos + ret + tmp); - ceph_zero_page_vector_range(page_align + read + ret, - tmp, pages); - ret += tmp; + pos + ret, pos + ret + zlen); + ceph_zero_page_vector_range(zoff, zlen, pages); + ret += zlen; } didpages = (page_align + ret) >> PAGE_CACHE_SHIFT; @@ -421,19 +531,19 @@ static ssize_t ceph_sync_read(struct kio if (file->f_flags & O_DIRECT) { while (iov_iter_count(i)) { - void __user *data = i->iov[0].iov_base + i->iov_offset; - size_t len = i->iov[0].iov_len - i->iov_offset; - - num_pages = calc_pages_for((unsigned long)data, len); - pages = ceph_get_direct_page_vector(data, - num_pages, true); + int page_align; + size_t len; + + len = dio_get_pagevlen(i); + pages = dio_alloc_pagev(i, len, true, &page_align, + &num_pages); if (IS_ERR(pages)) return PTR_ERR(pages); ret = striped_read(inode, off, len, pages, num_pages, checkeof, - 1, (unsigned long)data & ~PAGE_MASK); - ceph_put_page_vector(pages, num_pages, true); + 1, page_align); + dio_free_pagev(pages, num_pages, true); if (ret <= 0) break; @@ -570,10 +680,7 @@ ceph_sync_direct_write(struct kiocb *ioc iov_iter_init(&i, iov, nr_segs, count, 0); while (iov_iter_count(&i) > 0) { - void __user *data = i.iov->iov_base + i.iov_offset; - u64 len = i.iov->iov_len - i.iov_offset; - - page_align = (unsigned long)data & ~PAGE_MASK; + u64 len = dio_get_pagevlen(&i); snapc = ci->i_snap_realm->cached_context; vino = ceph_vino(inode); @@ -589,8 +696,7 @@ ceph_sync_direct_write(struct kiocb *ioc break; } - num_pages = calc_pages_for(page_align, len); - pages = ceph_get_direct_page_vector(data, num_pages, false); + pages = dio_alloc_pagev(&i, len, false, &page_align, &num_pages); if (IS_ERR(pages)) { ret = PTR_ERR(pages); goto out; @@ -612,7 +718,7 @@ ceph_sync_direct_write(struct kiocb *ioc if (!ret) ret = ceph_osdc_wait_request(&fsc->client->osdc, req); - ceph_put_page_vector(pages, num_pages, false); + dio_free_pagev(pages, num_pages, false); out: ceph_osdc_put_request(req); -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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