[Devel] [PATCH RHEL7 COMMIT] fuse kio: Move it variable from stack to struct fiemap_iterator

[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 dab15b6bdd2775117b060a81545280a010743e48
Author: Kirill Tkhai <ktkhai at virtuozzo.com>
Date:   Wed Sep 5 13:06:35 2018 +0300

    fuse kio: Move it variable from stack to struct fiemap_iterator
    
    This is just a preparation for next patches.
    
    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 | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/fs/fuse/kio/pcs/pcs_cluster.c b/fs/fuse/kio/pcs/pcs_cluster.c
index 088c18fccb18..35b222c7de75 100644
--- a/fs/fuse/kio/pcs/pcs_cluster.c
+++ b/fs/fuse/kio/pcs/pcs_cluster.c
@@ -85,6 +85,7 @@ struct fiemap_iterator
 
 	struct pcs_int_request	ireq;
 	pcs_api_iorequest_t	apireq;
+	struct iov_iter		it;
 };
 
 static void fiemap_iter_done(struct pcs_int_request * ireq)
@@ -236,7 +237,7 @@ static int fiemap_worker(void * arg)
 	struct pcs_int_request * orig_ireq = arg;
 	struct pcs_dentry_info * di;
 	struct fiemap_iterator * fiter;
-	struct iov_iter it;
+	struct iov_iter *it;
 
 	fiter = kmalloc(sizeof(struct fiemap_iterator), GFP_KERNEL);
 	if (fiter == NULL) {
@@ -244,6 +245,7 @@ static int fiemap_worker(void * arg)
 		ireq_complete(orig_ireq);
 		return 0;
 	}
+	it = &fiter->it;
 
 	fiter->orig_ireq = orig_ireq;
 	init_waitqueue_head(&fiter->wq);
@@ -264,8 +266,8 @@ static int fiemap_worker(void * arg)
 		return 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;
+	orig_ireq->apireq.req->get_iter(orig_ireq->apireq.req->datasource, 0, it);
+	fiter->mapped = &((struct fiemap*)it->data)->fm_mapped_extents;
 
 	fiemap_process_one(fiter);