linux-ext4 - Re: [PATCH] ext4: add more tracepoints and change to use MAJOR/MINOR dev macros

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Message-ID: <20110322015027.GB3907@thunk.org>
Date:	Mon, 21 Mar 2011 21:50:27 -0400
From:	Ted Ts'o <tytso@....edu>
To:	Jiaying Zhang <jiayingz@...gle.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext4: add more tracepoints and change to use
 MAJOR/MINOR dev macros

Added to the ext4 patch queue.  After running pahole, though, I'm
still noticing a lot of holes in the ftrace structures:

struct ftrace_raw_ext4_load_inode {
        struct trace_entry         ent;                  /*     0    12 */

        /* XXX 4 bytes hole, try to pack */

        ino_t                      ino;                  /*    16     8 */
        dev_t                      dev;                  /*    24     4 */
        char                       __data[0];            /*    28     0 */

        /* size: 32, cachelines: 1 */
        /* sum members: 24, holes: 1, sum holes: 4 */
        /* padding: 4 */
        /* last cacheline: 32 bytes */
};      /* definitions: 1 */

Simply by swapping the ino and dev fields means that we'll save 4
bytes for this event.

						- Ted

On Thu, Mar 17, 2011 at 07:13:25PM -0700, Jiaying Zhang wrote:
> ext4: add more tracepoints and change to use MAJOR/MINOR dev macros
> 
> - Add more ext4 tracepoints.
> - Change ext4 tracepoints to use dev_t field with MAJOR/MINOR macros
> so that we can save 4 bytes on certain platforms.
> - Add sync_mode to ext4_da_writepages, ext4_da_write_pages, and
> ext4_da_writepages_result tracepoints. Also remove for_reclaim
> field from ext4_da_writepages since it is usually not very useful.
> 
> Signed-off-by: Jiaying Zhang <jiayingz@...gle.com>


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