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Message-ID: <3DF95416.7010107@ToughGuy.net>
Date: Fri, 13 Dec 2002 08:59:26 +0530
From: Bourne <bourne@ToughGuy.net>
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To: linux-kernel@vger.kernel.org
Subject: 2.4.19 ( try_to_swap_out) does not set page->mapping to NULL
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Hi all, A small piece of code in mm/vmscan.c kept me confused. Please 
could some one explain this ?

File: mm/vmscan.c , try_to_swap_out()

....SNIP....
drop_pte: mm->rss--
                UnlockPage(page);
                ---SNIP--
                page_cache_release(page);
                return freeable;
                ----SNIP----
if(page->mapping)
    goto drop_pte;

What i can get is if page->mapping is NOT NULL , then do a 
page_cache_release(). This boils down to __free_pages_ok(). Here the 
code snippet is if(page->mapping) BUG();

So if try_to_swap_out wants to drop a page which can be brought in 
always ( i.e , not dirty ), then what is the harm in setting it to NULL ?

TIA

Bourne