Posix: Optimize posix code to improve file creation

Problem: Before executing a fop in POSIX xlator it builds an internal
         path based on GFID.To validate the path it call's (l)stat
         system call and while .glusterfs is heavily loaded kernel takes
         time to lookup inode and due to that performance drops

Solution: In this patch we followed two ways to improve the performance.
          1) Keep open fd specific to first level directory(gfid[0])
             in .glusterfs, it would force to kernel keep the inodes
             from all those files in cache. In case of memory pressure
             kernel won't uncache first level inodes. We need to open
             256 fd's per brick to access the entry faster.
          2) Use at based call's to access relative path to reduce
             path based lookup time.

Note: To verify the patch we have executed kernel untar 100 times on 6
      different clients after enabling metadata group-cache and some
      other option.We were getting more than 20 percent improvement in
      kenel untar after applying the patch.

Credits: Xavi Hernandez <xhernandez@redhat.com>
Change-Id: I1643e6b01ed669b2bb148d02f4e6a8e08da45343
updates: #891
Signed-off-by: Mohit Agrawal <moagrawal@redhat.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/xlators/storage/posix/src/posix.h b/xlators/storage/posix/src/posix.h
index fb609dff731..662b5c69f8a 100644
--- a/xlators/storage/posix/src/posix.h
+++ b/xlators/storage/posix/src/posix.h
@@ -152,7 +152,7 @@ struct posix_private {
 
     char *trash_path;
     /* lock for brick dir */
-    DIR *mount_lock;
+    int mount_lock;
 
     struct stat handledir;
 
@@ -214,6 +214,8 @@ struct posix_private {
     mode_t create_mask;
     mode_t create_directory_mask;
     uint32_t max_hardlinks;
+    int32_t arrdfd[256];
+    int dirfd;
 
     /* This option is used for either to call a landfill_purge or not */
     gf_boolean_t disable_landfill_purge;
@@ -331,6 +333,7 @@ posix_istat(xlator_t *this, inode_t *inode, uuid_t gfid, const char *basename,
 int
 posix_pstat(xlator_t *this, inode_t *inode, uuid_t gfid, const char *real_path,
             struct iatt *iatt, gf_boolean_t inode_locked);
+
 dict_t *
 posix_xattr_fill(xlator_t *this, const char *path, loc_t *loc, fd_t *fd,
                  int fdnum, dict_t *xattr, struct iatt *buf);