[Devel] [PATCH RHEL7 COMMIT] fuse kio: Move fiter ireq iocount assignment

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-862.11.6.vz7.71.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-862.11.6.vz7.71.8
------>
commit 480e0661677015b7a7ceab9760fbb3f2deee351f
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Wed Sep 5 13:06:37 2018 +0300

    fuse kio: Move fiter ireq iocount assignment
    
    The previous iteration finishes with "iocount == 0",
    so we have to initialize it only once.
    
    Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
    Acked-by: Alexey Kuznetsov <kuznet at virtuozzo.com>
    
    =====================
    Patchset description:
    
    Optimize fiemap ioctl
    
    https://jira.sw.ru/browse/HCI-90
    
    Summary:
      This patch set optimizes fiemap ioctl by removing
      kthread creation. Instead of this, static work
      is used, so we safe some time on copy_process().
    
    Fiemap does not require separate kthread, since
    the most time the kthread is spending in waiting
    for fiter->ireq.iocount becomes 0. Instead of this,
    the generic kthread could queue another fiemap
    requests at this time. This is the thing the patch set
    introduces.
    
    Note, that we had a kthread for every fiemap request,
    and this may look more scalable. But this is not true,
    since the actions, fiemap does, is pretty small. So,
    I think for the most workload the single fiemap work
    is enough. If we meet a workload, where the single
    work is not enough, it will be pretty easy to make
    fiemap_work just as an array in struct pcs_cluster_core
    (to make it per-node or even per-cpu). But I think,
    it's not necessary at least till main_job or completion_job
    are per-node or per-cpu (fiemap requests are small subset
    of all requests going through main_job).
    
    https://github.com/shekkbuilder/fiemap/blob/master/fiemap.c
    code was taken as a base for the performance test and modified.
    The below is results and the test's code.
    
    Time of test execution on 3 extents-file (just randomly chosen
    number of extents):
    
    Before: real 0m11.069s
    After:  real 0m9.112s
    
    It became 17% faster, it was 21% slower.
    
    Kirill Tkhai (7):
          fuse kio: Extract fiemap iteration from fiemap_worker() to separate function
          fuse kio: Move it variable from stack to struct fiemap_iterator
          fuse kio: Kill fiemap_worker() thread
          fuse kio: Move position advance in fiemap_process_one()
          fuse kio: Move fiter ireq iocount assignment
          fuse kio: Introduce fiemap_work
          fuse kio: Async queueing of fiemap from work
---
 fs/fuse/kio/pcs/pcs_cluster.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_cluster.c b/fs/fuse/kio/pcs/pcs_cluster.c
index 31cc93fd201d..e182a34cd16c 100644
--- a/fs/fuse/kio/pcs/pcs_cluster.c
+++ b/fs/fuse/kio/pcs/pcs_cluster.c
@@ -207,8 +207,6 @@ static void fiemap_process_one(struct fiemap_iterator *fiter)
 			goto out;
 		}
 
-		atomic_set(&fiter->ireq.iocount, 0);
-
 		sreq->dentry = di;
 		sreq->type = PCS_IREQ_IOCHUNK;
 		INIT_LIST_HEAD(&sreq->tok_list);
@@ -272,6 +270,7 @@ static void process_ireq_fiemap(struct pcs_int_request *orig_ireq)
 		kfree(fiter);
 		return;
 	}
+	atomic_set(&fiter->ireq.iocount, 0);
 	fiter->fiemap_max = orig_ireq->apireq.aux;
 	orig_ireq->apireq.req->get_iter(orig_ireq->apireq.req->datasource, 0, it);
 	fiter->mapped = &((struct fiemap*)it->data)->fm_mapped_extents;