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authorJan Kara <jack@suse.cz>2021-09-03 00:53:04 +0300
committerLinus Torvalds <torvalds@linux-foundation.org>2021-09-03 19:58:10 +0300
commit633a2abb9e1cd5c95f3b600f4b2c12cce22ae4a0 (patch)
treea7ff91638eb5b03dca868ec1be8a6bdff4b9b5c8
parenteb2169cee36fc492407a2d483c286b977a46288a (diff)
downloadlinux-633a2abb9e1cd5c95f3b600f4b2c12cce22ae4a0.tar.xz
writeback: track number of inodes under writeback
Patch series "writeback: Fix bandwidth estimates", v4. Fix estimate of writeback throughput when device is not fully busy doing writeback. Michael Stapelberg has reported that such workload (e.g. generated by linking) tends to push estimated throughput down to 0 and as a result writeback on the device is practically stalled. The first three patches fix the reported issue, the remaining two patches are unrelated cleanups of problems I've noticed when reading the code. This patch (of 4): Track number of inodes under writeback for each bdi_writeback structure. We will use this to decide whether wb does any IO and so we can estimate its writeback throughput. In principle we could use number of pages under writeback (WB_WRITEBACK counter) for this however normal percpu counter reads are too inaccurate for our purposes and summing the counter is too expensive. Link: https://lkml.kernel.org/r/20210713104519.16394-1-jack@suse.cz Link: https://lkml.kernel.org/r/20210713104716.22868-1-jack@suse.cz Signed-off-by: Jan Kara <jack@suse.cz> Cc: Wu Fengguang <fengguang.wu@intel.com> Cc: Michael Stapelberg <stapelberg+linux@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/fs-writeback.c5
-rw-r--r--include/linux/backing-dev-defs.h1
-rw-r--r--mm/backing-dev.c1
-rw-r--r--mm/page-writeback.c22
4 files changed, 27 insertions, 2 deletions
diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 4c3370548982..7439ecd44ac9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -406,6 +406,11 @@ static bool inode_do_switch_wbs(struct inode *inode,
inc_wb_stat(new_wb, WB_WRITEBACK);
}
+ if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
+ atomic_dec(&old_wb->writeback_inodes);
+ atomic_inc(&new_wb->writeback_inodes);
+ }
+
wb_get(new_wb);
/*
diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 1d7edad9914f..06fb8e13f6bc 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -116,6 +116,7 @@ struct bdi_writeback {
struct list_head b_dirty_time; /* time stamps are dirty */
spinlock_t list_lock; /* protects the b_* lists */
+ atomic_t writeback_inodes; /* number of inodes under writeback */
struct percpu_counter stat[NR_WB_STAT_ITEMS];
unsigned long congested; /* WB_[a]sync_congested flags */
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index f5561ea7d90a..b4c707ddedb1 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -293,6 +293,7 @@ static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,
INIT_LIST_HEAD(&wb->b_dirty_time);
spin_lock_init(&wb->list_lock);
+ atomic_set(&wb->writeback_inodes, 0);
wb->bw_time_stamp = jiffies;
wb->balanced_dirty_ratelimit = INIT_BW;
wb->dirty_ratelimit = INIT_BW;
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 9f63548f247c..e1aa1c9d8e36 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2731,6 +2731,16 @@ int clear_page_dirty_for_io(struct page *page)
}
EXPORT_SYMBOL(clear_page_dirty_for_io);
+static void wb_inode_writeback_start(struct bdi_writeback *wb)
+{
+ atomic_inc(&wb->writeback_inodes);
+}
+
+static void wb_inode_writeback_end(struct bdi_writeback *wb)
+{
+ atomic_dec(&wb->writeback_inodes);
+}
+
int test_clear_page_writeback(struct page *page)
{
struct address_space *mapping = page_mapping(page);
@@ -2752,6 +2762,9 @@ int test_clear_page_writeback(struct page *page)
dec_wb_stat(wb, WB_WRITEBACK);
__wb_writeout_inc(wb);
+ if (!mapping_tagged(mapping,
+ PAGECACHE_TAG_WRITEBACK))
+ wb_inode_writeback_end(wb);
}
}
@@ -2794,8 +2807,13 @@ int __test_set_page_writeback(struct page *page, bool keep_write)
PAGECACHE_TAG_WRITEBACK);
xas_set_mark(&xas, PAGECACHE_TAG_WRITEBACK);
- if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT)
- inc_wb_stat(inode_to_wb(inode), WB_WRITEBACK);
+ if (bdi->capabilities & BDI_CAP_WRITEBACK_ACCT) {
+ struct bdi_writeback *wb = inode_to_wb(inode);
+
+ inc_wb_stat(wb, WB_WRITEBACK);
+ if (!on_wblist)
+ wb_inode_writeback_start(wb);
+ }
/*
* We can come through here when swapping anonymous