Subject: Re: [PATCH] 2.6.14 patch for supporting madvise(MADV_FREE)
From: Badari Pulavarty <pbadari@us.ibm.com>
To: Andrea Arcangeli <andrea@suse.de>
Cc: lkml <linux-kernel@vger.kernel.org>, Hugh Dickins <hugh@veritas.com>,
       akpm@osdl.org, dvhltc@us.ibm.com, linux-mm <linux-mm@kvack.org>,
       Blaisorblade <blaisorblade@yahoo.it>, Jeff Dike <jdike@addtoit.com>
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Date: Wed, 02 Nov 2005 07:49:12 -0800
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On Wed, 2005-11-02 at 02:43 +0100, Andrea Arcangeli wrote:
> On Tue, Nov 01, 2005 at 05:15:01PM -0800, Badari Pulavarty wrote:
> > Here is the patch to support madvise(MADV_FREE) - which frees 
> > up the given range of pages and truncates the underlying backing 
> > store. This basically provides "punch hole into file" functionality.
> > Currently it supports ONLY shmfs/tmpfs - where we have short term 
> > need. Other filesystems return -ENOSYS.
> 
> MADV_FREE as a name isn't right if we return -ENOSYS for anonymoys
> memory.
> 
> MADV_FREE in other OS works _only_ on anonymous memory and returns
> -EINVAL if used on filebacked vmas. Infact we probably should rename our
> MADV_DONTNEED to MADV_FREE.
> 
> http://docs.sun.com/app/docs/doc/816-5168/6mbb3hrde?a=view
> 
> 	"This value cannot be used on mappings that have underlying file objects."
> 
> Our MADV_DONTNEED exactly matches the MADV_FREE semantics, and it seems
> the MADV_DONTNEED of other OS isn't destructive like ours. Except our
> MADV_DONTNEED also works on filebacked mappings but it's destructive
> only on anonymous memory.
> 
> 
> I thought Andrew suggested MADV_REMOVE for the new feature.

Yep. My bad. Andrew did suggest MADV_REMOVE. Let me rename and
generate patch once again !! Thanks for pointing out.

> 
> This feature didn't exist in other OS yet AFIK, so a new MADV_name for
> it makes sense. I'm not completely against extending MADV_FREE but then we
> shouldn't return -ENOSYS on anonymous memory and we should do the same
> thing MADV_DONTNEED does on anonymous memory. Probably a new name is
> safer to avoid confusion (think an application running MADV_FREE and
> expecting -EINVAL when used on filebacked mappings).
> 
> Thanks!
> 

Thanks,
Badari

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