To allow precise tracking of page caches accessed, add new tracepoints that trigger when a process actually accesses them. The ureadahead program used by ChromeOS traces the disk access of programs as they start up at boot up. It uses mincore(2) or the 'mm_filemap_add_to_page_cache' trace event to accomplish this. It stores this information in a "pack" file and on subsequent boots, it will read the pack file and call readahead(2) on the information so that disk storage can be loaded into RAM before the applications actually need it. A problem we see is that due to the kernel's readahead algorithm that can aggressively pull in more data than needed (to try and accomplish the same goal) and this data is also recorded. The end result is that the pack file contains a lot of pages on disk that are never actually used. Calling readahead(2) on these unused pages can slow down the system boot up times. To solve this, add 3 new trace events, get_pages, map_pages, and fault. These will be used to trace the pages are not only pulled in from disk, but are actually used by the application. Only those pages will be stored in the pack file, and this helps out the performance of boot up. With the combination of these 3 new trace events and mm_filemap_add_to_page_cache, we observed a reduction in the pack file by 7.3% - 20% on ChromeOS varying by device. Signed-off-by: Takaya Saeki <takayas@xxxxxxxxxxxx> --- Changelog between v2 and v1 - Fix a file offset type usage by casting pgoff_t to loff_t - Fixed format string of dev and inode include/trace/events/filemap.h | 84 ++++++++++++++++++++++++++++++++++ mm/filemap.c | 4 ++ 2 files changed, 88 insertions(+) V1:https://lore.kernel.org/all/20240618093656.1944210-1-takayas@xxxxxxxxxxxx/ diff --git a/include/trace/events/filemap.h b/include/trace/events/filemap.h index 46c89c1e460c..3a94bd633bf0 100644 --- a/include/trace/events/filemap.h +++ b/include/trace/events/filemap.h @@ -56,6 +56,90 @@ DEFINE_EVENT(mm_filemap_op_page_cache, mm_filemap_add_to_page_cache, TP_ARGS(folio) ); +DECLARE_EVENT_CLASS(mm_filemap_op_page_cache_range, + + TP_PROTO( + struct address_space *mapping, + pgoff_t index, + pgoff_t last_index + ), + + TP_ARGS(mapping, index, last_index), + + TP_STRUCT__entry( + __field(unsigned long, i_ino) + __field(dev_t, s_dev) + __field(unsigned long, index) + __field(unsigned long, last_index) + ), + + TP_fast_assign( + __entry->i_ino = mapping->host->i_ino; + if (mapping->host->i_sb) + __entry->s_dev = + mapping->host->i_sb->s_dev; + else + __entry->s_dev = mapping->host->i_rdev; + __entry->index = index; + __entry->last_index = last_index; + ), + + TP_printk( + "dev=%d:%d ino=%lx ofs=%lld max_ofs=%lld", + MAJOR(__entry->s_dev), + MINOR(__entry->s_dev), __entry->i_ino, + ((loff_t)__entry->index) << PAGE_SHIFT, + ((loff_t)__entry->last_index) << PAGE_SHIFT + ) +); + +DEFINE_EVENT(mm_filemap_op_page_cache_range, mm_filemap_get_pages, + TP_PROTO( + struct address_space *mapping, + pgoff_t index, + pgoff_t last_index + ), + TP_ARGS(mapping, index, last_index) +); + +DEFINE_EVENT(mm_filemap_op_page_cache_range, mm_filemap_map_pages, + TP_PROTO( + struct address_space *mapping, + pgoff_t index, + pgoff_t last_index + ), + TP_ARGS(mapping, index, last_index) +); + +TRACE_EVENT(mm_filemap_fault, + TP_PROTO(struct address_space *mapping, pgoff_t index), + + TP_ARGS(mapping, index), + + TP_STRUCT__entry( + __field(unsigned long, i_ino) + __field(dev_t, s_dev) + __field(unsigned long, index) + ), + + TP_fast_assign( + __entry->i_ino = mapping->host->i_ino; + if (mapping->host->i_sb) + __entry->s_dev = + mapping->host->i_sb->s_dev; + else + __entry->s_dev = mapping->host->i_rdev; + __entry->index = index; + ), + + TP_printk( + "dev=%d:%d ino=%lx ofs=%lld", + MAJOR(__entry->s_dev), + MINOR(__entry->s_dev), __entry->i_ino, + ((loff_t)__entry->index) << PAGE_SHIFT + ) +); + TRACE_EVENT(filemap_set_wb_err, TP_PROTO(struct address_space *mapping, errseq_t eseq), diff --git a/mm/filemap.c b/mm/filemap.c index 876cc64aadd7..39f9d7fb3d2c 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2556,6 +2556,7 @@ static int filemap_get_pages(struct kiocb *iocb, size_t count, goto err; } + trace_mm_filemap_get_pages(mapping, index, last_index); return 0; err: if (err < 0) @@ -3286,6 +3287,8 @@ vm_fault_t filemap_fault(struct vm_fault *vmf) if (unlikely(index >= max_idx)) return VM_FAULT_SIGBUS; + trace_mm_filemap_fault(mapping, index); + /* * Do we have something in the page cache already? */ @@ -3652,6 +3655,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, } while ((folio = next_uptodate_folio(&xas, mapping, end_pgoff)) != NULL); add_mm_counter(vma->vm_mm, folio_type, rss); pte_unmap_unlock(vmf->pte, vmf->ptl); + trace_mm_filemap_map_pages(mapping, start_pgoff, end_pgoff); out: rcu_read_unlock(); -- 2.45.2.627.g7a2c4fd464-goog
