On Wed, 26 Jun 2024 21:31:57 +0900 Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx> wrote: > On Thu, 20 Jun 2024 16:19:03 +0000 > Takaya Saeki <takayas@xxxxxxxxxxxx> 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) <mhiramat@xxxxxxxxxx> 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@xxxxxxxxxxx> -- Steve
