[PATCH 3/5] btrfs: add manual PSI accounting for compressed reads

[Christoph Hellwig]

btrfs compressed reads try to always read the entire compressed chunk,
even if only a subset is requested.  Currently this is covered by the
magic PSI accounting underneath submit_bio, but that is about to go
away. Instead add manual psi_memstall_{enter,leave} annotations.

Note that for readahead this really should be using readahead_expand,
but the additionals reads are also done for plain ->read_folio where
readahead_expand can't work, so this overall logic is left as-is for
now.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 fs/btrfs/compression.c | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
index e84d22c5c6a83..f7889a00e0055 100644
--- a/fs/btrfs/compression.c
+++ b/fs/btrfs/compression.c
@@ -15,6 +15,7 @@
 #include <linux/string.h>
 #include <linux/backing-dev.h>
 #include <linux/writeback.h>
+#include <linux/psi.h>
 #include <linux/slab.h>
 #include <linux/sched/mm.h>
 #include <linux/log2.h>
@@ -519,7 +520,8 @@ static u64 bio_end_offset(struct bio *bio)
  */
 static noinline int add_ra_bio_pages(struct inode *inode,
 				     u64 compressed_end,
-				     struct compressed_bio *cb)
+				     struct compressed_bio *cb,
+				     unsigned long *pflags)
 {
 	struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
 	unsigned long end_index;
@@ -588,6 +590,9 @@ static noinline int add_ra_bio_pages(struct inode *inode,
 			continue;
 		}
 
+		if (unlikely(PageWorkingset(page)))
+			psi_memstall_enter(pflags);
+
 		ret = set_page_extent_mapped(page);
 		if (ret < 0) {
 			unlock_page(page);
@@ -674,6 +679,8 @@ void btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 	u64 em_len;
 	u64 em_start;
 	struct extent_map *em;
+	/* initialize to 1 to make skip psi_memstall_leave unless needed */
+	unsigned long pflags = 1;
 	blk_status_t ret;
 	int ret2;
 	int i;
@@ -729,7 +736,7 @@ void btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		goto fail;
 	}
 
-	add_ra_bio_pages(inode, em_start + em_len, cb);
+	add_ra_bio_pages(inode, em_start + em_len, cb, &pflags);
 
 	/* include any pages we added in add_ra-bio_pages */
 	cb->len = bio->bi_iter.bi_size;
@@ -810,6 +817,9 @@ void btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
 		}
 	}
 
+	if (!pflags)
+		psi_memstall_leave(&pflags);
+
 	if (refcount_dec_and_test(&cb->pending_ios))
 		finish_compressed_bio_read(cb);
 	return;
-- 
2.30.2