[PATCH 4/5] erofs: add manual PSI accounting for the compressed address space

Christoph Hellwig
2022-09-15T09:42:25Z

erofs uses an additional address space for compressed data read from disk
in addition to the one directly associated with the inode. Reading into
the lower address space is open coded using add_to_page_cache_lru instead
of using the filemap.c helper for page allocation micro-optimizations,
which means it is not covered by the MM PSI annotations for ->read_folio
and ->readahead, so add manual ones instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Gao Xiang <hsiangkao@linux.alibaba.com>
---
fs/erofs/zdata.c | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
index 5792ca9e0d5ef..143a101a36887 100644
--- a/fs/erofs/zdata.c
+++ b/fs/erofs/zdata.c
@@ -7,6 +7,7 @@
#include "zdata.h"
#include "compress.h"
#include <linux/prefetch.h>
+#include <linux/psi.h>

#include <trace/events/erofs.h>

@@ -1365,6 +1366,8 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
struct block_device *last_bdev;
unsigned int nr_bios = 0;
struct bio *bio = NULL;
+ /* initialize to 1 to make skip psi_memstall_leave unless needed */
+ unsigned long pflags = 1;

bi_private = jobqueueset_init(sb, q, fgq, force_fg);
qtail[JQ_BYPASS] = &q[JQ_BYPASS]->head;
@@ -1414,10 +1417,15 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
if (bio && (cur != last_index + 1 ||
last_bdev != mdev.m_bdev)) {
submit_bio_retry:
+ if (!pflags)
+ psi_memstall_leave(&pflags);
submit_bio(bio);
bio = NULL;
}

+ if (unlikely(PageWorkingset(page)))
+ psi_memstall_enter(&pflags);
+
if (!bio) {
bio = bio_alloc(mdev.m_bdev, BIO_MAX_VECS,
REQ_OP_READ, GFP_NOIO);
@@ -1445,8 +1453,11 @@ static void z_erofs_submit_queue(struct z_erofs_decompress_frontend *f,
move_to_bypass_jobqueue(pcl, qtail, owned_head);
} while (owned_head != Z_EROFS_PCLUSTER_TAIL);

- if (bio)
+ if (bio) {
+ if (!pflags)
+ psi_memstall_leave(&pflags);
submit_bio(bio);
+ }

/*
* although background is preferred, no one is pending for submission.
--
2.30.2