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Subject: Re: [RFC PATCH] LTTng instrumentation mm (updated)
From: Dave Hansen <haveblue@us.ibm.com>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
       linux-mm@kvack.org, mbligh@google.com
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Date: Fri, 30 Nov 2007 09:46:41 -0800
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On Fri, 2007-11-30 at 11:11 -0500, Mathieu Desnoyers wrote:
> +static inline swp_entry_t page_swp_entry(struct page *page)
> +{
> +       swp_entry_t entry;
> +       VM_BUG_ON(!PageSwapCache(page));
> +       entry.val = page_private(page);
> +       return entry;
> +}

This probably needs to be introduced (and used) in a separate patch.
Please fix up those other places in the code that can take advantage of
it.

>  #ifdef CONFIG_MIGRATION
>  static inline swp_entry_t make_migration_entry(struct page *page, int
> write)
>  {
> Index: linux-2.6-lttng/mm/swapfile.c
> ===================================================================
> --- linux-2.6-lttng.orig/mm/swapfile.c  2007-11-30 09:18:38.000000000
> -0500
> +++ linux-2.6-lttng/mm/swapfile.c       2007-11-30 10:21:50.000000000
> -0500
> @@ -1279,6 +1279,7 @@ asmlinkage long sys_swapoff(const char _
>         swap_map = p->swap_map;
>         p->swap_map = NULL;
>         p->flags = 0;
> +       trace_mark(mm_swap_file_close, "filp %p", swap_file);
>         spin_unlock(&swap_lock);
>         mutex_unlock(&swapon_mutex);
>         vfree(swap_map);
> @@ -1660,6 +1661,8 @@ asmlinkage long sys_swapon(const char __
>         } else {
>                 swap_info[prev].next = p - swap_info;
>         }
> +       trace_mark(mm_swap_file_open, "filp %p filename %s",
> +               swap_file, name); 

You print out the filp a number of times here, but how does that help in
a trace?  If I was trying to figure out which swapfile, I'd probably
just want to know the swp_entry_t->type, then I could look at this:

dave@foo:~/garbage$ cat /proc/swaps 
Filename                                Type            Size    Used    Priority
/dev/sda2                               partition       1992052 649336  -1

to see the ordering.

-- Dave