On Thu, Oct 13, 2016 at 11:44:41AM +0200, Jan Kara wrote:

On Thu 15-09-16 14:54:59, Kirill A. Shutemov wrote:

quoted

We writeback whole huge page a time.

This is one of the things I don't understand. Firstly I didn't see where
changes of writeback like this would happen (maybe they come later).
Secondly I'm not sure why e.g. writeback should behave atomically wrt huge
pages. Is this because radix-tree multiorder entry tracks dirtiness for us
at that granularity?

We track dirty/writeback on per-compound pages: meaning we have one
dirty/writeback flag for whole compound page, not on every individual
4k subpage. The same story for radix-tree tags.

BTW, can you also explain why do we need multiorder entries? What do
they solve for us?

It helps us having coherent view on tags in radix-tree: no matter which
index we refer from the range huge page covers we will get the same
answer on which tags set.

I'm sorry for these basic questions but I'd just like to understand how is
this supposed to work...

								Honza

quoted

Signed-off-by: Kirill A. Shutemov <redacted>
---
 mm/filemap.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/filemap.c b/mm/filemap.c
index 05b42d3e5ed8..53da93156e60 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c

@@ -372,9 +372,14 @@ static int __filemap_fdatawait_range(struct address_space *mapping,
 			if (page->index > end)
 				continue;
 
+			page = compound_head(page);
 			wait_on_page_writeback(page);
 			if (TestClearPageError(page))
 				ret = -EIO;
+			if (PageTransHuge(page)) {
+				index = page->index + HPAGE_PMD_NR;
+				i += index - pvec.pages[i]->index - 1;
+			}
 		}
 		pagevec_release(&pvec);
 		cond_resched();

-- 
2.9.3

-- 
Jan Kara [off-list ref]
SUSE Labs, CR

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-- 
 Kirill A. Shutemov