linux-kernel - Re: [PATCH 4/5] mm: simplify reclaim path for MADV

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Date:	Tue, 27 Oct 2015 15:39:16 +0800
From:	yalin wang <yalin.wang2010@...il.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	Johannes Weiner <hannes@...xchg.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 4/5] mm: simplify reclaim path for MADV_FREE


> On Oct 27, 2015, at 15:09, Minchan Kim <minchan@...nel.org> wrote:
> 
> Hello Yalin,
> 
> Sorry for missing you in Cc list.
> IIRC, mails to send your previous mail address(Yalin.Wang@...ymobile.com)
> were returned.
> 
> You added comment bottom line so I'm not sure what PageDirty you meant.
> 
>> it is wrong here if you only check PageDirty() to decide if the page is freezable or not .
>> The Anon page are shared by multiple process, _mapcount > 1 ,
>> so you must check all pt_dirty bit during page_referenced() function,
>> see this mail thread:
>> http://ns1.ske-art.com/lists/kernel/msg1934021.html
> 
> If one of pte among process sharing the page was dirty, the dirtiness should
> be propagated from pte to PG_dirty by try_to_unmap_one.
> IOW, if the page doesn't have PG_dirty flag, it means all of process did
> MADV_FREE.
> 
> Am I missing something from you question?
> If so, could you show exact scenario I am missing?
> 
> Thanks for the interest.
oh, yeah , that is right , i miss that , pte_dirty will propagate to PG_dirty ,
so that is correct .
Generic to say this patch move set_page_dirty() from add_to_swap() to 
try_to_unmap(), i think can change a little about this patch:

@@ -1476,6 +1446,8 @@ static int try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
				ret = SWAP_FAIL;
				goto out_unmap;
			}
+			if (!PageDirty(page))
+				SetPageDirty(page);
			if (list_empty(&mm->mmlist)) {
				spin_lock(&mmlist_lock);
				if (list_empty(&mm->mmlist))

i think this 2 lines can be removed ,
since  pte_dirty have propagated to set_page_dirty() , we don’t need this line here ,
otherwise you will always dirty a AnonPage, even it is clean,
then we will page out this clean page to swap partition one more , this is not needed.
am i understanding correctly ?

By the way, please change my mail address to yalin.wang2010@...il.com in CC list .
Thanks a lot. :) 

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