[ltt-dev] [PATCH] Add tracepoints to track pagecache transition

[Mathieu Desnoyers]

* Atsushi Tsuji (a-tsuji at bk.jp.nec.com) wrote:
> Hi,
>
> 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.
>
> I attached an example which is visualization of pagecache status using
> SystemTap. That graph describes pagecache transition of File A and File B
> on a file-by-file basis with the situation where regular I/O to File A
> is delayed because of other I/O to File B. We visually understand
> pagecache for File A is narrowed down due to I/O pressure from File B.
>
> The below patch is for lttng tree to add those new tracepoints.
>
> Signed-off-by: Atsushi Tsuji <a-tsuji at bk.jp.nec.com>

Hi Atsushi,

This patch looks good, thanks ! I'll merge it.

Please fix the settings of you mail client for the next patches, because
it seems to have problems with line-wrap. Lines longer than 80 columns
are wrapped, which makes patch application a bit more difficult.

Thanks,

Mathieu

> ---
> diff --git a/include/trace/filemap.h b/include/trace/filemap.h
> index 0d881a1..454d908 100644
> --- a/include/trace/filemap.h
> +++ b/include/trace/filemap.h
> @@ -9,5 +9,11 @@ DECLARE_TRACE(wait_on_page_start,
>  DECLARE_TRACE(wait_on_page_end,
>  	TPPROTO(struct page *page, int bit_nr),
>  	TPARGS(page, bit_nr));
> +DECLARE_TRACE(add_to_page_cache,
> +	TPPROTO(struct address_space *mapping, pgoff_t offset),
> +	TPARGS(mapping, offset));
> +DECLARE_TRACE(remove_from_page_cache,
> +	TPPROTO(struct address_space *mapping),
> +	TPARGS(mapping));
>
>  #endif
> diff --git a/ltt/probes/mm-trace.c b/ltt/probes/mm-trace.c
> index 2b60d89..b3122c9 100644
> --- a/ltt/probes/mm-trace.c
> +++ b/ltt/probes/mm-trace.c
> @@ -164,6 +164,22 @@ void probe_swap_file_open(struct file *file, char *filename)
>  }
>  #endif
>
> +void probe_add_to_page_cache(struct address_space *mapping, pgoff_t offset)
> +{
> +	trace_mark_tp(mm, add_to_page_cache, add_to_page_cache,
> +		probe_add_to_page_cache,
> +		"inode %lu sdev %u",
> +		mapping->host->i_ino, mapping->host->i_sb->s_dev);
> +}
> +
> +void probe_remove_from_page_cache(struct address_space *mapping)
> +{
> +	trace_mark_tp(mm, remove_from_page_cache, remove_from_page_cache,
> +		probe_remove_from_page_cache,
> +		"inode %lu sdev %u",
> +		mapping->host->i_ino, mapping->host->i_sb->s_dev);
> +}
> +
>  MODULE_LICENSE("GPL");
>  MODULE_AUTHOR("Mathieu Desnoyers");
>  MODULE_DESCRIPTION("MM Tracepoint Probes");
> diff --git a/mm/filemap.c b/mm/filemap.c
> index cca96ed..7f3fbcf 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -45,6 +45,8 @@
>
>  DEFINE_TRACE(wait_on_page_start);
>  DEFINE_TRACE(wait_on_page_end);
> +DEFINE_TRACE(add_to_page_cache);
> +DEFINE_TRACE(remove_from_page_cache);
>
>  /*
>   * Shared mappings implemented 30.11.1994. It's not fully working yet,
> @@ -123,6 +125,7 @@ void __remove_from_page_cache(struct page *page)
>  	page->mapping = NULL;
>  	mapping->nrpages--;
>  	__dec_zone_page_state(page, NR_FILE_PAGES);
> +	trace_remove_from_page_cache(mapping);
>  	BUG_ON(page_mapped(page));
>
>  	/*
> @@ -477,6 +480,7 @@ 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_add_to_page_cache(mapping, offset);
>  		} else {
>  			page->mapping = NULL;
>  			mem_cgroup_uncharge_cache_page(page);
>
>



-- 
Mathieu Desnoyers
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