lkml.org 
[lkml]   [2007]   [Mar]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Linux page cache issue?
From
Date
On Wed, 2007-03-28 at 02:45 -0400, Xin Zhao wrote:
> 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.

Yes.

> 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()

A comment from the top of fs/dcache.c:

/*
* Notes on the allocation strategy:
*
* The dcache is a master of the icache - whenever a dcache entry
* exists, the inode will always exist. "iput()" is done either when
* the dcache entry is deleted or garbage collected.
*/

Basically, as long a a dentry is present, iput_final won't be called on
the 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

Shaggy
--
David Kleikamp
IBM Linux Technology Center

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-03-28 16:13    [W:0.148 / U:0.036 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site