Re: [PATCH] Add tracepoints to track pagecache transition

Peter Zijlstra
2009-02-17T09:33:49Z

On Tue, 2009-02-17 at 18:00 +0900, Atsushi Tsuji wrote:

> The below patch adds instrumentation for pagecache.

And somehow you forgot to CC any of the mm people.. ;-)

> I thought it would be useful to trace pagecache behavior for problem
> analysis (performance bottlenecks, behavior differences between stable
> time and trouble time).
>
> By using those tracepoints, we can describe and visualize pagecache
> transition (file-by-file basis) in kernel and pagecache
> consumes most of the memory in running system and pagecache hit rate
> and writeback behavior will influence system load and performance.

> Signed-off-by: Atsushi Tsuji <a-tsuji@bk.jp.nec.com>
> ---
> diff --git a/include/trace/filemap.h b/include/trace/filemap.h
> new file mode 100644
> index 0000000..196955e
> --- /dev/null
> +++ b/include/trace/filemap.h
> @@ -0,0 +1,13 @@
> +#ifndef _TRACE_FILEMAP_H
> +#define _TRACE_FILEMAP_H
> +
> +#include <linux/tracepoint.h>
> +
> +DECLARE_TRACE(filemap_add_to_page_cache,
> + TPPROTO(struct address_space *mapping, pgoff_t offset),
> + TPARGS(mapping, offset));
> +DECLARE_TRACE(filemap_remove_from_page_cache,
> + TPPROTO(struct address_space *mapping),
> + TPARGS(mapping));

This is rather asymmetric, why don't we care about the offset for the
removed page?

> +#endif
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 23acefe..76a6887 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -34,6 +34,7 @@
> #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
> #include <linux/memcontrol.h>
> #include <linux/mm_inline.h> /* for page_is_file_cache() */
> +#include <trace/filemap.h>
> #include "internal.h"
>
> /*
> @@ -43,6 +44,8 @@
>
> #include <asm/mman.h>
>
> +DEFINE_TRACE(filemap_add_to_page_cache);
> +DEFINE_TRACE(filemap_remove_from_page_cache);
>
> /*
> * Shared mappings implemented 30.11.1994. It's not fully working yet,
> @@ -120,6 +123,7 @@ void __remove_from_page_cache(struct page *page)
> page->mapping = NULL;
> mapping->nrpages--;
> __dec_zone_page_state(page, NR_FILE_PAGES);
> + trace_filemap_remove_from_page_cache(mapping);
> BUG_ON(page_mapped(page));
> mem_cgroup_uncharge_cache_page(page);
>
> @@ -475,6 +479,7 @@ int add_to_page_cache_locked(struct page *page, struct address_space *mapping,
> if (likely(!error)) {
> mapping->nrpages++;
> __inc_zone_page_state(page, NR_FILE_PAGES);
> + trace_filemap_add_to_page_cache(mapping, offset);
> } else {
> page->mapping = NULL;
> mem_cgroup_uncharge_cache_page(page);