[Devel] [PATCH RHEL7 COMMIT] ms/block: add REQ_BACKGROUND

[Konstantin Khorenko]

The commit is pushed to "branch-rh7-3.10.0-1062.1.2.vz7.114.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1062.1.2.vz7.114.9
------>
commit 4fef686179897b6c5bfaacbe19a8a231b4e214d4
Author: Jens Axboe <axboe at fb.com>
Date:   Fri Oct 25 13:17:20 2019 +0300

    ms/block: add REQ_BACKGROUND
    
    This adds a new request flag, REQ_BACKGROUND, that callers can use to
    tell the block layer that this is background (non-urgent) IO.
    
    Signed-off-by: Jens Axboe <axboe at fb.com>
    Reviewed-by: Christoph Hellwig <hch at lst.de>
    
    https://jira.sw.ru/browse/PSBM-96243
    
    (cherry picked from commit 1d796d6a9641fbfcd90fcfaf6fb4894a13d0304f)
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    
    =====================
    Patchset description:
    
    block: backport writeback throttling
    
    We have a problem that if we run heavy write load on one cpu
    simultaneousely with short direct reads on other cpu, the latter will
    hang significantly. Writeback throttling looks like a sollution for
    these reads, as it will decrease the priority of long running writeback.
    
    Running simple dd experiment we see that reads latency decreased after
    wbt patches applied:
    https://docs.google.com/spreadsheets/d/1HLtepwFL_N5zm0JcTqMtJoYnf-b6Slwld8DDgL0gNDI
    
    We've ran vconsolidate on custom kernel with these patches, though it
    does not show any performance improvement (likely because this test does
    not produce high rate of writeback), it does not crash or fail the test.
    
    https://jira.sw.ru/browse/PSBM-96243
    
    Jens Axboe (6):
      block: add REQ_BACKGROUND
      writeback: add wbc_to_write_flags()
      writeback: mark background writeback as such
      writeback: track if we're sleeping on progress in
        balance_dirty_pages()
      blk-wbt: add general throttling mechanism
      block: hook up writeback throttling
    
    Omar Sandoval (1):
      block: get rid of struct blk_issue_stat
    
    Pavel Tikhomirov (2):
      x86/asm: remove the unused get_limit() method
      block: enable CONFIG_BLK_WBT*
      blk-wbt: increase maximum queue depth to increase performance of writes
---
 include/linux/blk_types.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index c0e1caa89985..aecb3b0e21a6 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -189,6 +189,7 @@ enum rq_flag_bits {
 
 	/* bio only flags */
 	__REQ_RAHEAD,		/* read ahead, can fail anytime */
+	__REQ_BACKGROUND,	/* background IO */
 	__REQ_THROTTLED,	/* This bio has already been subjected to
 				 * throttling rules. Don't do it again. */
 
@@ -231,6 +232,7 @@ enum rq_flag_bits {
 #define REQ_DISCARD		(1ULL << __REQ_DISCARD)
 #define REQ_WRITE_SAME		(1ULL << __REQ_WRITE_SAME)
 #define REQ_NOIDLE		(1ULL << __REQ_NOIDLE)
+#define REQ_BACKGROUND		(1ULL << __REQ_BACKGROUND)
 
 #define REQ_FAILFAST_MASK \
 	(REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)