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

[Mathieu Desnoyers]

* Mathieu Desnoyers (compudj at krystal.dyndns.org) wrote:
> * 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.
> >
> 
> Hi Atsushi,
> 
> Great patch !
> 
> I'll merge it into the next LTTng release.
> 

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Thanks,

Mathieu


> Thanks,
> 
> Mathieu
> 
> > Signed-off-by: Atsushi Tsuji <a-tsuji at bk.jp.nec.com>
> > ---
> > 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);
> >
> >
> 
> 
> > _______________________________________________
> > ltt-dev mailing list
> > ltt-dev at lists.casi.polymtl.ca
> > http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
> 
> 
> -- 
> Mathieu Desnoyers
> OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68
> 
> _______________________________________________
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> ltt-dev at lists.casi.polymtl.ca
> http://lists.casi.polymtl.ca/cgi-bin/mailman/listinfo/ltt-dev
> 

-- 
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F  BA06 3F25 A8FE 3BAE 9A68