[Devel] [PATCH RHEL COMMIT] mm, cgroup, writeback: Enable per-cgroup writeback for v1 cgroup.

[Konstantin Khorenko]

The commit is pushed to "branch-rh9-5.14.vz9.1.x-ovz" and will appear at https://src.openvz.org/scm/ovz/vzkernel.git
after ark-5.14
------>
commit 6790531d9a5b424dd2d4025cda8bf6cf23cf3b0a
Author: Andrey Ryabinin <ryabinin.a.a at gmail.com>
Date:   Thu Sep 30 17:43:59 2021 +0300

    mm, cgroup, writeback: Enable per-cgroup writeback for v1 cgroup.
    
    Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
    
    Cherry-picked from vz8 commit 9dd7b6eebb0d ("mm, cgroup, writeback:
    Enable per-cgroup writeback for v1 cgroup.")).
    
    Updated to follow upstream commits ed7b6b4f6e91 ("bdi: remove
    BDI_CAP_CGROUP_WRITEBACK")) and f56753ac2a90 ("bdi: replace
    BDI_CAP_NO_{WRITEBACK,ACCT_DIRTY} with a single flag")).
    
    Signed-off-by: Nikita Yushchenko <nikita.yushchenko at virtuozzo.com>
---
 include/linux/backing-dev.h | 4 +---
 mm/memcontrol.c             | 2 +-
 mm/vmscan.c                 | 2 +-
 3 files changed, 3 insertions(+), 5 deletions(-)

diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 44df4fcef65c..6eb5b52cf105 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -193,9 +193,7 @@ static inline bool inode_cgwb_enabled(struct inode *inode)
 {
 	struct backing_dev_info *bdi = inode_to_bdi(inode);
 
-	return cgroup_subsys_on_dfl(memory_cgrp_subsys) &&
-		cgroup_subsys_on_dfl(io_cgrp_subsys) &&
-		(bdi->capabilities & BDI_CAP_WRITEBACK) &&
+	return (bdi->capabilities & BDI_CAP_WRITEBACK) &&
 		(inode->i_sb->s_iflags & SB_I_CGROUPWB);
 }
 
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 492e4b4e7574..d51f09a70bcd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -418,7 +418,7 @@ struct cgroup_subsys_state *mem_cgroup_css_from_page(struct page *page)
 
 	memcg = page_memcg(page);
 
-	if (!memcg || !cgroup_subsys_on_dfl(memory_cgrp_subsys))
+	if (!memcg || 0 /*!cgroup_subsys_on_dfl(memory_cgrp_subsys))*/)
 		memcg = root_mem_cgroup;
 
 	return &memcg->css;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 41f05cf20599..f55e24e18874 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -447,7 +447,7 @@ static bool writeback_throttling_sane(struct scan_control *sc)
 	if (!cgroup_reclaim(sc))
 		return true;
 #ifdef CONFIG_CGROUP_WRITEBACK
-	if (cgroup_subsys_on_dfl(memory_cgrp_subsys))
+	if (1/*cgroup_subsys_on_dfl(memory_cgrp_subsys)*/)
 		return true;
 #endif
 	return false;