+Cc Daniel, On 6/22/26 15:15, Zhan Xusheng wrote: > 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. >
Cc: [email protected] > Fixes: cb8ff3ead9a3 ("f2fs: add page-order information for large folio reads > in iostat") > Signed-off-by: Zhan Xusheng <[email protected]> > --- > 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..cd801bd0b910 100644 > --- a/fs/f2fs/iostat.c > +++ b/fs/f2fs/iostat.c > @@ -188,6 +188,12 @@ void f2fs_update_read_folio_count(struct f2fs_sb_info > *sbi, struct folio *folio) > unsigned int order = folio_order(folio); > unsigned long flags; > > + /* > + * 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); What do you think of relocating this into f2fs_init_iostat()? Thanks, > + > if (!sbi->iostat_enable) > return; > > 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
