On Thu, 20 Jun 2024 16:19:03 +0000 Takaya Saeki <taka...@chromium.org> wrote:
> 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. > This looks good to me from the trace-event point of view. Reviewed-by: Masami Hiramatsu (Google) <mhira...@kernel.org> Thanks! > Signed-off-by: Takaya Saeki <taka...@chromium.org> > --- > 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-taka...@chromium.org/ > > 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 > -- Masami Hiramatsu (Google) <mhira...@kernel.org>
