[Devel] [PATCH RHEL9 COMMIT] dm-ploop: rework logic in pio processing

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.0-427.44.1.vz9.80.x-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh9-5.14.0-427.44.1.vz9.80.6
------>
commit 56504024d8de6fe86135e798de90370d87099714
Author: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
Date:   Fri Jan 24 17:36:30 2025 +0200

    dm-ploop: rework logic in pio processing
    
    improve how and when we wait for pios to complete
    before proceeding with next pios.
    force writing of pending md pages in case we have a sync pios.
    remove now unused functions.
    
    https://virtuozzo.atlassian.net/browse/VSTOR-91821
    Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
    
    ======
    Patchset description:
    ploop: optimistations and scalling
    
    Ploop processes requsts in a different threads in parallel
    where possible which results in significant improvement in
    performance and makes further optimistations possible.
    
    Known bugs:
      - delayed metadata writeback is not working and is missing error handling
         - patch to disable it until fixed
      - fast path is not working - causes rcu lockups - patch to disable it
    
    Further improvements:
      - optimize md pages lookups
    
    Alexander Atanasov (50):
      dm-ploop: md_pages map all pages at creation time
      dm-ploop: Use READ_ONCE/WRITE_ONCE to access md page data
      dm-ploop: fsync after all pios are sent
      dm-ploop: move md status to use proper bitops
      dm-ploop: convert wait_list and wb_batch_llist to use lockless lists
      dm-ploop: convert enospc handling to use lockless lists
      dm-ploop: convert suspended_pios list to use lockless list
      dm-ploop: convert the rest of the lists to use llist variant
      dm-ploop: combine processing of pios thru prepare list and remove
        fsync worker
      dm-ploop: move from wq to kthread
      dm-ploop: move preparations of pios into the caller from worker
      dm-ploop: fast path execution for reads
      dm-ploop: do not use a wrapper for set_bit to make a page writeback
      dm-ploop: BAT use only one list for writeback
      dm-ploop: make md writeback timeout to be per page
      dm-ploop: add interface to disable bat writeback delay
      dm-ploop: convert wb_batch_list to lockless variant
      dm-ploop: convert high_prio to status
      dm-ploop: split cow processing into two functions
      dm-ploop: convert md page rw lock to spin lock
      dm-ploop: convert bat_rwlock to bat_lock spinlock
      dm-ploop: prepare bat updates under bat_lock
      dm-ploop: make ploop_bat_write_complete ready for parallel pio
        completion
      dm-ploop: make ploop_submit_metadata_writeback return number of
        requests sent
      dm-ploop: introduce pio runner threads
      dm-ploop: add pio list ids to be used when passing pios to runners
      dm-ploop: process pios via runners
      dm-ploop: disable metadata writeback delay
      dm-ploop: disable fast path
      dm-ploop: use lockless lists for chained cow updates list
      dm-ploop: use lockless lists for data ready pios
      dm-ploop: give runner threads better name
      dm-ploop: resize operation - add holes bitmap locking
      dm-ploop: remove unnecessary operations
      dm-ploop: use filp per thread
      dm-ploop: catch if we try to advance pio past bio end
      dm-ploop: support REQ_FUA for data pios
      dm-ploop: proplerly access nr_bat_entries
      dm-ploop: fix locking and improve error handling when submitting pios
      dm-ploop: fix how ENOTBLK is handled
      dm-ploop: sync when suspended or stopping
      dm-ploop: rework bat completion logic
      dm-ploop: rework logic in pio processing
      dm-ploop: end fsync pios in parallel
      dm-ploop: make filespace preallocations async
      dm-ploop: resubmit enospc pios from dispatcher thread
      dm-ploop: dm-ploop: simplify discard completion
      dm-ploop: use GFP_ATOMIC instead of GFP_NOIO
      dm-ploop: fix locks used in mixed context
      dm-ploop: fix how current flags are managed inside threads
    
    Andrey Zhadchenko (13):
      dm-ploop: do not flush after metadata writes
      dm-ploop: set IOCB_DSYNC on all FUA requests
      dm-ploop: remove extra ploop_cluster_is_in_top_delta()
      dm-ploop: introduce per-md page locking
      dm-ploop: reduce BAT accesses on discard completion
      dm-ploop: simplify llseek
      dm-ploop: speed up ploop_prepare_bat_update()
      dm-ploop: make new allocations immediately visible in BAT
      dm-ploop: drop ploop_cluster_is_in_top_delta()
      dm-ploop: do not wait for BAT update for non-FUA requests
      dm-ploop: add delay for metadata writeback
      dm-ploop: submit all postponed metadata on REQ_OP_FLUSH
      dm-ploop: handle REQ_PREFLUSH
    
    Feature: dm-ploop: ploop target driver
---
 drivers/md/dm-ploop-map.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
index 35d12fd54050..f9904e708c35 100644
--- a/drivers/md/dm-ploop-map.c
+++ b/drivers/md/dm-ploop-map.c
@@ -2049,6 +2049,7 @@ void do_ploop_run_work(struct ploop *ploop)
 	struct llist_node *llflush_pios;
 	unsigned int old_flags = current->flags;
 	int npios;
+	int force_md_update;
 
 	current->flags |= PF_IO_THREAD|PF_LOCAL_THROTTLE|PF_MEMALLOC_NOIO;
 
@@ -2064,8 +2065,7 @@ void do_ploop_run_work(struct ploop *ploop)
 		ploop_runners_add_work_list(ploop, lldeferred_pios);
 
 	if (llembedded_pios)
-		ploop_prepare_embedded_pios(ploop, llist_reverse_order(llembedded_pios),
-					    &deferred_pios);
+		ploop_prepare_embedded_pios(ploop, llembedded_pios, &deferred_pios);
 
 	llflush_pios = llist_del_all(&ploop->pios[PLOOP_LIST_FLUSH]);
 
@@ -2080,23 +2080,28 @@ void do_ploop_run_work(struct ploop *ploop)
 	if (llcow_pios)
 		ploop_runners_add_work_list(ploop, llcow_pios);
 
-	/* wait for all pios to be executed before metadata updates */
+	/*
+	 * put stick in the wheel - wait for all pios to be executed before doing metadata
+	 * we could gain a bit more iops if we can skip this wait but for now we can not
+	 */
 	current->flags = old_flags;
-	wait_event_interruptible(ploop->dispatcher_wq_data, (!ploop_runners_have_pending(ploop)));
+	wait_event_interruptible(ploop->dispatcher_wq_data,
+				 (!ploop_runners_have_pending(ploop)));
 	current->flags |= PF_IO_THREAD|PF_LOCAL_THROTTLE|PF_MEMALLOC_NOIO;
 
 	/* if we have a flush we must sync md data too */
-	npios = ploop_submit_metadata_writeback(ploop, !!llflush_pios | ploop->force_md_writeback);
+	force_md_update = !!llflush_pios | ploop->force_md_writeback;
+	npios = ploop_submit_metadata_writeback(ploop, force_md_update);
 
-	if (llflush_pios) {
-		if (npios) {
-			/* wait for metadata writeback to complete */
-			current->flags = old_flags;
-			/* First wait all pios to be processed */
-			wait_event_interruptible(ploop->dispatcher_wq_data,
-						 (!ploop_runners_have_pending(ploop)));
-			current->flags |= PF_IO_THREAD|PF_LOCAL_THROTTLE|PF_MEMALLOC_NOIO;
-		}
+	if (npios) {
+		/* wait for metadata writeback to complete */
+		current->flags = old_flags;
+		/* First wait all pios to be processed */
+		wait_event_interruptible(ploop->dispatcher_wq_data,
+					 (!ploop_runners_have_pending(ploop)));
+		current->flags |= PF_IO_THREAD|PF_LOCAL_THROTTLE|PF_MEMALLOC_NOIO;
+	}
+	if (llflush_pios || npios) {
 		/* Now process fsync pios after we have done all other */
 		npios = process_ploop_fsync_work(ploop, llflush_pios);
 		/* Since dispatcher is single thread no other work can be queued */