The patch titled
knfsd: stop NFSD writes from being broken into lots of little writes to filesystem
has been added to the -mm tree. Its filename is
knfsd-stop-nfsd-writes-from-being-broken-into-lots-of-little-writes-to-filesystem.patch
*** Remember to use Documentation/SubmitChecklist when testing your code ***
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: knfsd: stop NFSD writes from being broken into lots of little writes to filesystem
From: NeilBrown <neilb@xxxxxxx>
When NFSD receives a write request, the data is typically in a number of
1448 byte segments and writev is used to collect them together.
Unfortunately, generic_file_buffered_write passes these to the filesystem
one at a time, so an e.g. 32K over-write becomes a series of partial-page
writes to each page, causing the filesystem to have to pre-read those pages
- wasted effort.
generic_file_buffered_write handles one segment of the vector at a time as
it has to pre-fault in each segment to avoid deadlocks. When writing from
kernel-space (and nfsd does) this is not an issue, so
generic_file_buffered_write does not need to break and iovec from nfsd into
little pieces.
This patch avoids the splitting when get_fs is KERNEL_DS as it is
from NFSd.
This issue was introduced by commit 6527c2bdf1f833cc18e8f42bd97973d583e4aa83
Acked-by: Nick Piggin <nickpiggin@xxxxxxxxxxxx>
Cc: Norman Weathers <norman.r.weathers@xxxxxxxxxxxxxxxxxx>
Cc: Vladimir V. Saveliev <vs@xxxxxxxxxxx>
Signed-off-by: Neil Brown <neilb@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 32 +++++++++++++++++++-------------
1 files changed, 19 insertions(+), 13 deletions(-)
diff -puN mm/filemap.c~knfsd-stop-nfsd-writes-from-being-broken-into-lots-of-little-writes-to-filesystem mm/filemap.c
--- a/mm/filemap.c~knfsd-stop-nfsd-writes-from-being-broken-into-lots-of-little-writes-to-filesystem
+++ a/mm/filemap.c
@@ -2033,21 +2033,27 @@ generic_file_buffered_write(struct kiocb
/* Limit the size of the copy to the caller's write size */
bytes = min(bytes, count);
- /*
- * Limit the size of the copy to that of the current segment,
- * because fault_in_pages_readable() doesn't know how to walk
- * segments.
+ /* We only need to worry about prefaulting when writes are from
+ * user-space. NFSd uses vfs_writev with several non-aligned
+ * segments in the vector, and limiting to one segment a time is
+ * a noticeable performance for re-write
*/
- bytes = min(bytes, cur_iov->iov_len - iov_base);
-
- /*
- * Bring in the user page that we will copy from _first_.
- * Otherwise there's a nasty deadlock on copying from the
- * same page as we're writing to, without it being marked
- * up-to-date.
- */
- fault_in_pages_readable(buf, bytes);
+ if (!segment_eq(get_fs(), KERNEL_DS)) {
+ /*
+ * Limit the size of the copy to that of the current
+ * segment, because fault_in_pages_readable() doesn't
+ * know how to walk segments.
+ */
+ bytes = min(bytes, cur_iov->iov_len - iov_base);
+ /*
+ * Bring in the user page that we will copy from
+ * _first_. Otherwise there's a nasty deadlock on
+ * copying from the same page as we're writing to,
+ * without it being marked up-to-date.
+ */
+ fault_in_pages_readable(buf, bytes);
+ }
page = __grab_cache_page(mapping,index,&cached_page,&lru_pvec);
if (!page) {
status = -ENOMEM;
_
Patches currently in -mm which might be from neilb@xxxxxxx are
origin.patch
knfsd-fix-return-value-for-writes-to-some-files-in-nfsd-filesystem.patch
knfsd-tidy-up-choice-of-filesystem-identifier-when-creating-a-filehandle.patch
knfsd-add-some-new-fsid-types.patch
knfsd-allow-the-server-to-provide-a-gid-list-when-using-auth_unix-authentication.patch
sysctl-remove-insert_at_head-from-register_sysctl.patch
revert-md-avoid-possible-bug_on-in-md-bitmap-handling-for-git-block.patch
replace-highest_possible_node_id-with-nr_node_ids.patch
convert-highest_possible_processor_id-to-nr_cpu_ids.patch
fix-quadratic-behavior-of-shrink_dcache_parent.patch
knfsd-nfsd4-fix-non-terminated-string.patch
knfsd-nfsd4-relax-checking-of-acl-inheritance-bits.patch
knfsd-nfsd4-simplify-nfsv4-posix-translation.patch
knfsd-nfsd4-represent-nfsv4-acl-with-array-instead-of-linked-list.patch
knfsd-nfsd4-fix-memory-leak-on-kmalloc-failure-in-savemem.patch
knfsd-nfsd4-fix-error-return-on-unsupported-acl.patch
knfsd-nfsd4-acls-dont-return-explicit-mask.patch
knfsd-nfsd4-acls-avoid-unnecessary-denies.patch
knfsd-nfsd4-fix-handling-of-directories-without-default-acls.patch
knfsd-stop-nfsd-writes-from-being-broken-into-lots-of-little-writes-to-filesystem.patch
readahead-nfsd-case.patch
readahead-nfsd-case-fix.patch
drivers-mdc-use-array_size-macro-when-appropriate.patch
md-dm-reduce-stack-usage-with-stacked-block-devices.patch
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