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

[Atsushi Tsuji]

Mathieu Desnoyers wrote:
> * 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.
>>
> 
> -EDOESNOTAPPLY
> 
> Please make sure your email client is correctly configured and try to
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> 

Hi Mathieu,

Sorry for wrong patch. I resend fixed one.

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);