[PATCH 1/1] UBUNTU: SAUCE: add tracing for user initiated readahead requests

[Andy Whitcroft]

Track pages which undergo readahead and for each record which were
actually consumed, via either read or faulted into a map.  This allows
userspace readahead applications (such as ureadahead) to track which
pages in core at the end of a boot are actually required and generate an
optimal readahead pack.  It also allows pack adjustment and optimisation
in parallel with readahead, allowing the pack to evolve to be accurate
as userspace paths change.  The status of the pages are reported back via
the mincore() call using a newly allocated bit.

Signed-off-by: Andy Whitcroft <apw at canonical.com>
---
 include/linux/page-flags.h |    3 +++
 mm/filemap.c               |    3 +++
 mm/memory.c                |    7 ++++++-
 mm/mincore.c               |    2 ++
 mm/readahead.c             |    1 +
 5 files changed, 15 insertions(+), 1 deletions(-)

diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
index 5b59f35..89dc94f 100644
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -108,6 +108,7 @@ enum pageflags {
 #ifdef CONFIG_MEMORY_FAILURE
 	PG_hwpoison,		/* hardware poisoned page. Don't touch */
 #endif
+	PG_readaheadunused,	/* user oriented readahead as yet unused*/
 	__NR_PAGEFLAGS,
 
 	/* Filesystems */
@@ -239,6 +240,8 @@ PAGEFLAG(MappedToDisk, mappedtodisk)
 PAGEFLAG(Reclaim, reclaim) TESTCLEARFLAG(Reclaim, reclaim)
 PAGEFLAG(Readahead, reclaim)		/* Reminder to do async read-ahead */
 
+PAGEFLAG(ReadaheadUnused, readaheadunused)
+
 #ifdef CONFIG_HIGHMEM
 /*
  * Must use a macro here due to header dependency issues. page_zone() is not
diff --git a/mm/filemap.c b/mm/filemap.c
index 20e5642..26e5e15 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1192,6 +1192,9 @@ int file_read_actor(read_descriptor_t *desc, struct page *page,
 	if (size > count)
 		size = count;
 
+	if (PageReadaheadUnused(page))
+		ClearPageReadaheadUnused(page);
+
 	/*
 	 * Faults on the destination of a read are common, so do it before
 	 * taking the kmap.
diff --git a/mm/memory.c b/mm/memory.c
index 119b7cc..97ca21b 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2865,10 +2865,15 @@ static int __do_fault(struct mm_struct *mm, struct vm_area_struct *vma,
 	else
 		VM_BUG_ON(!PageLocked(vmf.page));
 
+	page = vmf.page;
+
+	/* Mark the page as used on fault. */
+	if (PageReadaheadUnused(page))
+		ClearPageReadaheadUnused(page);
+
 	/*
 	 * Should we do an early C-O-W break?
 	 */
-	page = vmf.page;
 	if (flags & FAULT_FLAG_WRITE) {
 		if (!(vma->vm_flags & VM_SHARED)) {
 			anon = 1;
diff --git a/mm/mincore.c b/mm/mincore.c
index 9ac42dc..a4e573a 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -77,6 +77,8 @@ static unsigned char mincore_page(struct address_space *mapping, pgoff_t pgoff)
 	page = find_get_page(mapping, pgoff);
 	if (page) {
 		present = PageUptodate(page);
+		if (present)
+			present |= (PageReadaheadUnused(page) << 7);
 		page_cache_release(page);
 	}
 
diff --git a/mm/readahead.c b/mm/readahead.c
index 77506a2..6948b92 100644
--- a/mm/readahead.c
+++ b/mm/readahead.c
@@ -181,6 +181,7 @@ __do_page_cache_readahead(struct address_space *mapping, struct file *filp,
 		list_add(&page->lru, &page_pool);
 		if (page_idx == nr_to_read - lookahead_size)
 			SetPageReadahead(page);
+		SetPageReadaheadUnused(page);
 		ret++;
 	}
 
-- 
1.7.0.4