On 03/11/2016 08:30 AM, Minchan Kim wrote:
Procedure of page migration is as follows: First of all, it should isolate a page from LRU and try to migrate the page. If it is successful, it releases the page for freeing. Otherwise, it should put the page back to LRU list. For LRU pages, we have used putback_lru_page for both freeing and putback to LRU list. It's okay because put_page is aware of LRU list so if it releases last refcount of the page, it removes the page from LRU list. However, It makes unnecessary operations (e.g., lru_cache_add, pagevec and flags operations.
Yeah, and compaction (perhaps also other migration users) has to drain the lru pvec... Getting rid of this stuff is worth even by itself.
It would be not significant but no worth to do) and harder to support new non-lru page migration because put_page isn't aware of non-lru page's data structure. To solve the problem, we can add new hook in put_page with PageMovable flags check but it can increase overhead in hot path and needs new locking scheme to stabilize the flag check with put_page. So, this patch cleans it up to divide two semantic(ie, put and putback). If migration is successful, use put_page instead of putback_lru_page and use putback_lru_page only on failure. That makes code more readable and doesn't add overhead in put_page.
I had an idea of checking for count==1 in putback_lru_page() which would take the put_page() shortcut from there. But maybe it can't be done nicely without races.
Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Signed-off-by: Minchan Kim <minchan@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx> Note in -next/after 4.6-rc1 this will need some rebasing though. _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
