linux-kernel - Re: [PATCH 2/12] mm: let swap use exceptional entries

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Date:	Sat, 18 Jun 2011 14:55:46 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hugh Dickins <hughd@...gle.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 2/12] mm: let swap use exceptional entries

On Tue, 14 Jun 2011 03:43:47 -0700 (PDT) Hugh Dickins <hughd@...gle.com> wrote:

> In an i386 kernel this limits its information (type and page offset)
> to 30 bits: given 32 "types" of swapfile and 4kB pagesize, that's
> a maximum swapfile size of 128GB.  Which is less than the 512GB we
> previously allowed with X86_PAE (where the swap entry can occupy the
> entire upper 32 bits of a pte_t), but not a new limitation on 32-bit
> without PAE; and there's not a new limitation on 64-bit (where swap
> filesize is already limited to 16TB by a 32-bit page offset).

hm.

>  Thirty
> areas of 128GB is probably still enough swap for a 64GB 32-bit machine.

What if it was only one area?  128GB is close enough to 64GB (or, more
realistically, 32GB) to be significant.  For the people out there who
are using a single 200GB swap partition and actually needed that much,
what happens?  swapon fails?

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