Re: [PATCH 1/3] When migrate_pages returns 0, all pages must have been released

On Thu, 20 Jan 2011, Andrea Arcangeli wrote:

Hello,

On Thu, Jan 20, 2011 at 11:30:35AM -0600, Christoph Lameter wrote:

quoted

On Fri, 21 Jan 2011, Minchan Kim wrote:

quoted

diff --git a/mm/migrate.c b/mm/migrate.c
index 46fe8cc..7d34237 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c

@@ -772,6 +772,7 @@ uncharge:
 unlock:
 	unlock_page(page);

+move_newpage:
 	if (rc != -EAGAIN) {
  		/*
  		 * A page that has been migrated has all references

@@ -785,8 +786,6 @@ unlock:
 		putback_lru_page(page);
 	}

-move_newpage:
-
 	/*
 	 * Move the new page to the LRU. If migration was not successful
 	 * then this will free the page.

What does this do? Not covered by the description.

It makes a difference for the two goto move_newpage, when rc =
0. Otherwise the function will return 0, despite
putback_lru_page(page) wasn't called (and the caller of migrate_pages
won't call putback_lru_pages if migrate_pages returned 0).

Think about the difference:

Moving the move_newpage will now cause another removal and freeing of the
page if rc != -EAGAIN.

The first goto move_newpage (because page count is 1) will now mean that
the page is freed twice. One because of the rc != EAGAIN branch and then
another time by the following putback_lru_page().


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