Message-ID: <4ae3c140703272345y3b3cb3cexf4c4b63e0035d5b9@mail.gmail.com>
Date:	Wed, 28 Mar 2007 02:45:23 -0400
From:	"Xin Zhao" <uszhaoxin@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	"Xin Zhao" <uszhaoxin@...il.com>
Subject: Linux page cache issue?

Hi,

If a Linux process opens and reads a file A, then it closes the file.
Will Linux keep the file A's data in cache for a while in case another
process opens and reads the same in a short time? I think that is what
I heard before.

But after I digged into the kernel code, I am confused.

When a process closes the file A, iput() will be called, which in turn
calls the follows two functions:
iput_final()->generic_drop_inode()

But from the following calling chain, we can see that file close will
eventually lead to evict and free all cached pages. Actually in
truncate_complete_page(), the pages will be freed.  This seems to
imply that Linux has to re-read the same data from disk even if
another process B read the same file right after process A closes the
file. That does not make sense to me.

/***calling chain ***/
generic_delete_inode/generic_forget_inode()->
truncate_inode_pages()->truncate_inode_pages_range()->
truncate_complete_page()->remove_from_page_cache()->
__remove_from_page_cache()->radix_tree_delete()

Am I missing something? Can someone please provide some advise?

Thanks a lot
-x
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