On Wed, 26 Jun 2024 21:31:57 +0900
Masami Hiramatsu (Google) [off-list ref] wrote:

On Thu, 20 Jun 2024 16:19:03 +0000
Takaya Saeki [off-list ref] wrote:

quoted

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) <mhiramat@kernel.org>

I added my reviewed-by on the last patch, you could have added it on
this one as it didn't change as much. But anyway, here it is again:

Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>

-- Steve