linux-kernel - Re: [PATCH] make MADV

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Date:	Thu, 12 Apr 2007 00:41:23 +0200
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Rik van Riel <riel@...hat.com>
CC:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: [PATCH] make MADV_FREE lazily free memory

Rik van Riel a écrit :
> Make it possible for applications to have the kernel free memory
> lazily.  This reduces a repeated free/malloc cycle from freeing
> pages and allocating them, to just marking them freeable.  If the
> application wants to reuse them before the kernel needs the memory,
> not even a page fault will happen.
> 

Hi Rik

I dont understand this last sentence. If not even a page fault happens, how 
the kernel knows that the page was eventually reused by the application, and 
should not be freed in case of memory pressure ?

ptr = mmap(some space);
madvise(ptr, length, MADV_FREE);
/* kernel may free the pages */
sleep(10);

/* what the application must do know before reusing space ? */
memset(ptr, data, 10000);
/* kernel should not free ptr[0..10000] now */

Thank you
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