Re: [PATCH v2 01/18] mm: use put_page to free page instead of putback_lru_page

[Minchan Kim <minchan@kernel.org>]

On Mon, Mar 21, 2016 at 04:13:43PM +0900, Chulmin Kim wrote:
> On 2016년 03월 21일 15:30, 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. 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.
> >
> >Comment from Vlastimil
> >"Yeah, and compaction (perhaps also other migration users) has to drain
> >the lru pvec... Getting rid of this stuff is worth even by itself."
> >
> >Cc: Mel Gorman <mgorman@suse.de>
> >Cc: Hugh Dickins <hughd@google.com>
> >Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> >Acked-by: Vlastimil Babka <vbabka@suse.cz>
> >Signed-off-by: Minchan Kim <minchan@kernel.org>
> >---
> >  mm/migrate.c | 50 +++++++++++++++++++++++++++++++-------------------
> >  1 file changed, 31 insertions(+), 19 deletions(-)
> >
> >diff --git a/mm/migrate.c b/mm/migrate.c
> >index 6c822a7b27e0..b65c84267ce0 100644
> >--- a/mm/migrate.c
> >+++ b/mm/migrate.c
> >@@ -913,6 +913,14 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
> >  		put_anon_vma(anon_vma);
> >  	unlock_page(page);
> >  out:
> >+	/* If migration is scucessful, move newpage to right list */
> 
> A minor comment fix :)
>  +	/* If migration is successful, move newpage to right list */

Hello Chulmin,

Fixed the typo.

Thanks for the review!

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