From: Hugh Dickins <hughd@google.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH 2/12] mm: let swap use exceptional entries
Date: Tue, 12 Jul 2011 15:35:41 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.00.1107121509230.2112@sister.anvils> (raw)
In-Reply-To: <20110618145546.12e175bf.akpm@linux-foundation.org>
On Sat, 18 Jun 2011, Andrew Morton wrote:
> On Tue, 14 Jun 2011 03:43:47 -0700 (PDT) Hugh Dickins <hughd@google.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?
No, it doesn't fail: it just trims back the amount of swap that is used
(and counted) to the maximum that the running kernel supports (just like
when you switch between 64bit and 32bit-PAE and 32bit-nonPAE kernels
using the same large swap device, the 64bit being able to access more
of it than the 32bit-PAE kernel, and that more than the 32bit-nonPAE).
I'd grown to think that the users of large amounts of RAM may like to
have a little swap for leeway, but live in dread of the slow death that a
large amount of swap can result in. Maybe that's just one class of user.
I'd worry more about this if it were a new limitation for 64bit; but it's
just a lower limitation for the 32bit-PAE case. If it actually proves
to be an issue (and we abandon our usual mantra to go to 64bit), then I
don't think having 32 distinct areas is sacrosanct: we can (configurably
or tunably) lower the number of areas and increase their size; but I
doubt we shall need to bother.
ARM is getting LPAE? Then I guess this is a good moment to enforce
the new limit.
Hugh
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next prev parent reply other threads:[~2011-07-12 22:35 UTC|newest]
Thread overview: 36+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-14 10:40 [PATCH 0/12] tmpfs: convert from old swap vector to radix tree Hugh Dickins
2011-06-14 10:42 ` [PATCH 1/12] radix_tree: exceptional entries and indices Hugh Dickins
2011-06-14 11:22 ` Pekka Enberg
2011-06-15 0:24 ` Hugh Dickins
2011-06-17 23:38 ` Andrew Morton
2011-06-18 0:07 ` Randy Dunlap
2011-06-18 0:12 ` Randy Dunlap
2011-06-18 1:52 ` Hugh Dickins
2011-07-19 22:36 ` Hugh Dickins
2011-07-19 23:28 ` Randy Dunlap
2011-06-18 0:13 ` Hugh Dickins
2011-06-18 21:48 ` Andrew Morton
2011-07-12 22:56 ` Hugh Dickins
2011-07-12 23:24 ` Andrew Morton
2011-07-13 22:27 ` Hugh Dickins
2011-06-14 10:43 ` [PATCH 2/12] mm: let swap use exceptional entries Hugh Dickins
2011-06-18 21:52 ` Andrew Morton
2011-07-12 22:08 ` Hugh Dickins
2011-07-13 23:11 ` Andrew Morton
2011-07-19 22:46 ` Hugh Dickins
2011-06-18 21:55 ` Andrew Morton
2011-07-12 22:35 ` Hugh Dickins [this message]
2011-06-14 10:45 ` [PATCH 3/12] tmpfs: demolish old swap vector support Hugh Dickins
2011-06-14 10:48 ` [PATCH 4/12] tmpfs: miscellaneous trivial cleanups Hugh Dickins
2011-06-14 10:49 ` [PATCH 5/12] tmpfs: copy truncate_inode_pages_range Hugh Dickins
2011-06-14 10:51 ` [PATCH 6/12] tmpfs: convert shmem_truncate_range to radix-swap Hugh Dickins
2011-06-14 10:52 ` [PATCH 7/12] tmpfs: convert shmem_unuse_inode " Hugh Dickins
2011-06-14 10:53 ` [PATCH 8/12] tmpfs: convert shmem_getpage_gfp " Hugh Dickins
2011-06-14 10:54 ` [PATCH 9/12] tmpfs: convert mem_cgroup shmem " Hugh Dickins
2011-06-14 10:56 ` [PATCH 10/12] tmpfs: convert shmem_writepage and enable swap Hugh Dickins
2011-06-14 10:57 ` [PATCH 11/12] tmpfs: use kmemdup for short symlinks Hugh Dickins
2011-06-14 11:16 ` Pekka Enberg
2011-06-14 10:59 ` [PATCH 12/12] mm: a few small updates for radix-swap Hugh Dickins
2011-06-15 0:49 ` [PATCH v2 " Hugh Dickins
2011-06-14 17:29 ` [PATCH 0/12] tmpfs: convert from old swap vector to radix tree Linus Torvalds
2011-06-14 18:20 ` Rik van Riel
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