linux-kernel - Re: [PATCH] include private data mappings in RLIMIT

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Date:	Tue, 10 Jul 2007 20:42:59 +0100 (BST)
From:	Hugh Dickins <hugh@...itas.com>
To:	Dave McCracken <dave.mccracken@...cle.com>
cc:	herbert.van.den.bergh@...cle.com, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH] include private data mappings in RLIMIT_DATA limit

On Tue, 10 Jul 2007, Dave McCracken wrote:
> On Tuesday 10 July 2007, Hugh Dickins wrote:
> >
> > Mapped private readonly yes, but vm_stat_account() says
> > 	if (file) {
> > 		mm->shared_vm += pages;
> > 		if ((flags & (VM_EXEC|VM_WRITE)) == VM_EXEC)
> > 			mm->exec_vm += pages;
> 
> In that code shared_vm includes everything that's mmap()ed, including private 
> mappings.  But if you look at Herbert's patch he has the following change:
> 
>         if (file) {
> -               mm->shared_vm += pages;
> +               if (flags & VM_SHARED)
> +                       mm->shared_vm += pages;
>                 if ((flags & (VM_EXEC|VM_WRITE)) == VM_EXEC)
>                         mm->exec_vm += pages;
> 
> This means that shared_vm now is truly only memory that's mapped VM_SHARED and 
> does not include VM_EXEC memory.  That necessitates the separate subtraction 
> of exec_vm in the data calculations.

Ah, I just noticed at the beginning of the patch, and didn't look for
a balancing change - thanks.  I'd strongly recommend that he not mess
around with these numbers, unless there's _very_ good reason: they're
not ideal, nothing ever will be, changing them around just causes pain.
shared_vm may not be a full description of what it counts, but it'll
do until you've a better name (readonly mappings share with the file
even when they're private).

Hugh
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