[PATCH v2] f2fs: don't drop the top folio order in the f2fs_iostat tracepoint
From: Zhan Xusheng <hidden>
Date: 2026-06-23 07:26:49
Also in:
lkml, stable
Subsystem:
f2fs file system, filesystems (vfs and infrastructure), the rest, tracing · Maintainers:
Jaegeuk Kim, Chao Yu, Alexander Viro, Christian Brauner, Linus Torvalds, Steven Rostedt, Masami Hiramatsu
The f2fs_iostat tracepoint stores the per-order read folio counts in a
fixed-size array and prints a fixed number of buckets, both hardcoded to
11. The sysfs iostat accounting array is instead sized by NR_PAGE_ORDERS
(= MAX_PAGE_ORDER + 1), which is not always 11:
arm64 16K pages -> MAX_PAGE_ORDER 11 -> NR_PAGE_ORDERS 12
arm64 64K pages -> MAX_PAGE_ORDER 13 -> NR_PAGE_ORDERS 14
f2fs enables large folios for immutable, non-compressed files, and the
read folio order is bounded by MAX_PAGECACHE_ORDER, i.e.
min(MAX_XAS_ORDER, PREFERRED_MAX_PAGECACHE_ORDER). With THP enabled this
reaches order 11 on 16K/64K base-page kernels (MAX_XAS_ORDER caps it at
11). So an order-11 read folio is possible there and is accounted into
index 11 of the array.
On those configurations the sysfs file reports the order-11 count
correctly, but the tracepoint silently drops it: the memcpy is capped at
min(NR_PAGE_ORDERS, 11), so index 11 is never copied and the trace
disagrees with sysfs. There is no memory-safety issue, only the order-11
bucket missing from the trace; 4K-page kernels (NR_PAGE_ORDERS == 11,
max order <= 9) are unaffected.
Size the array and the printed buckets by a ceiling that covers the
largest possible NR_PAGE_ORDERS (14) with headroom, and add a
BUILD_BUG_ON() so any future growth of NR_PAGE_ORDERS fails the build
loudly instead of silently truncating again. The human-readable
"order=count" output is preserved.
Fixes: cb8ff3ead9a3 ("f2fs: add page-order information for large folio reads in iostat")
Cc: stable@vger.kernel.org
Signed-off-by: Zhan Xusheng <redacted>
---
v2:
- Move the BUILD_BUG_ON() from f2fs_update_read_folio_count() into
f2fs_init_iostat() (Chao Yu)
- Add Cc: stable (Chao Yu)
fs/f2fs/iostat.c | 6 ++++++
include/trace/events/f2fs.h | 20 ++++++++++++++++----
2 files changed, 22 insertions(+), 4 deletions(-)
diff --git a/fs/f2fs/iostat.c b/fs/f2fs/iostat.c
index ae265e3e9b2c..12d4e18a6a50 100644
--- a/fs/f2fs/iostat.c
+++ b/fs/f2fs/iostat.c@@ -332,6 +332,12 @@ void f2fs_destroy_iostat_processing(void) int f2fs_init_iostat(struct f2fs_sb_info *sbi) { + /* + * The f2fs_iostat tracepoint emits a fixed number of read folio order + * buckets; make sure every order fits so none is silently dropped. + */ + BUILD_BUG_ON(NR_PAGE_ORDERS > F2FS_IOSTAT_RD_FOLIO_ORDERS); + /* init iostat info */ spin_lock_init(&sbi->iostat_lock); spin_lock_init(&sbi->iostat_lat_lock);
diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
index b5188d2671d7..3e810690d9de 100644
--- a/include/trace/events/f2fs.h
+++ b/include/trace/events/f2fs.h@@ -2114,6 +2114,14 @@ DEFINE_EVENT(f2fs_zip_end, f2fs_decompress_pages_end, ); #ifdef CONFIG_F2FS_IOSTAT +/* + * Number of read folio order buckets emitted by the f2fs_iostat tracepoint. + * TP_printk() cannot loop, so the field count is fixed here and must be >= + * the largest possible NR_PAGE_ORDERS (14 on arm64 with 64K pages). The + * BUILD_BUG_ON() in f2fs_update_read_folio_count() enforces this. + */ +#define F2FS_IOSTAT_RD_FOLIO_ORDERS 16 + TRACE_EVENT(f2fs_iostat, TP_PROTO(struct f2fs_sb_info *sbi, unsigned long long *iostat,
@@ -2151,7 +2159,7 @@ TRACE_EVENT(f2fs_iostat, __field(unsigned long long, fs_mrio) __field(unsigned long long, fs_discard) __field(unsigned long long, fs_reset_zone) - __array(unsigned long long, read_folio_count, 11) + __array(unsigned long long, read_folio_count, F2FS_IOSTAT_RD_FOLIO_ORDERS) ), TP_fast_assign(
@@ -2186,7 +2194,8 @@ TRACE_EVENT(f2fs_iostat, __entry->fs_reset_zone = iostat[FS_ZONE_RESET_IO]; memset(__entry->read_folio_count, 0, sizeof(__entry->read_folio_count)); memcpy(__entry->read_folio_count, read_folio_count, - sizeof(unsigned long long) * min_t(int, NR_PAGE_ORDERS, 11)); + sizeof(unsigned long long) * + min_t(int, NR_PAGE_ORDERS, F2FS_IOSTAT_RD_FOLIO_ORDERS)); ), TP_printk("dev = (%d,%d), "
@@ -2201,7 +2210,8 @@ TRACE_EVENT(f2fs_iostat, "fs [data=%llu, (gc_data=%llu, cdata=%llu), " "node=%llu, meta=%llu], " "read_folio_count [0=%llu, 1=%llu, 2=%llu, 3=%llu, 4=%llu, " - "5=%llu, 6=%llu, 7=%llu, 8=%llu, 9=%llu, 10=%llu]", + "5=%llu, 6=%llu, 7=%llu, 8=%llu, 9=%llu, 10=%llu, 11=%llu, " + "12=%llu, 13=%llu, 14=%llu, 15=%llu]", show_dev(__entry->dev), __entry->app_wio, __entry->app_dio, __entry->app_bio, __entry->app_mio, __entry->app_bcdio, __entry->app_mcdio, __entry->fs_dio, __entry->fs_cdio,
@@ -2218,7 +2228,9 @@ TRACE_EVENT(f2fs_iostat, __entry->read_folio_count[4], __entry->read_folio_count[5], __entry->read_folio_count[6], __entry->read_folio_count[7], __entry->read_folio_count[8], __entry->read_folio_count[9], - __entry->read_folio_count[10]) + __entry->read_folio_count[10], __entry->read_folio_count[11], + __entry->read_folio_count[12], __entry->read_folio_count[13], + __entry->read_folio_count[14], __entry->read_folio_count[15]) ); #ifndef __F2FS_IOSTAT_LATENCY_TYPE
--
2.43.0