Messages in this thread | | | From | Vlastimil Babka <> | Subject | Re: [PATCH v1 01/19] mm: use put_page to free page instead of putback_lru_page | Date | Mon, 14 Mar 2016 09:48:33 +0100 |
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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@suse.cz> > Cc: Mel Gorman <mgorman@suse.de> > Cc: Hugh Dickins <hughd@google.com> > Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> > Signed-off-by: Minchan Kim <minchan@kernel.org>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Note in -next/after 4.6-rc1 this will need some rebasing though.
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