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;
+ }
+
+ iov++;
+ data = iov->iov_base;
+ 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);
--
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