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 15:08:58 -0700 (PDT) [thread overview]
Message-ID: <alpine.LSU.2.00.1107121501100.2112@sister.anvils> (raw)
In-Reply-To: <20110618145254.1b333344.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:
>
> > --- linux.orig/mm/filemap.c 2011-06-13 13:26:44.430284135 -0700
> > +++ linux/mm/filemap.c 2011-06-13 13:27:34.526532556 -0700
> > @@ -717,9 +717,12 @@ repeat:
> > page = radix_tree_deref_slot(pagep);
> > if (unlikely(!page))
> > goto out;
> > - if (radix_tree_deref_retry(page))
> > + if (radix_tree_exception(page)) {
> > + if (radix_tree_exceptional_entry(page))
> > + goto out;
> > + /* radix_tree_deref_retry(page) */
> > goto repeat;
> > -
> > + }
> > if (!page_cache_get_speculative(page))
> > goto repeat;
>
> All the crap^Wnice changes made to filemap.c really need some comments,
> please. Particularly when they're keyed off the bland-sounding
> "radix_tree_exception()". Apparently they have something to do with
> swap, but how is the poor reader to know this?
The naming was intentionally bland, because other filesystems might
in future have other uses for such exceptional entries.
(I think the field size would generally defeat it, but you can,
for example, imagine a small filesystem wanting to save sector number
there when a page is evicted.)
But let's go bland when it's more familiar, and such uses materialize -
particularly since I only placed those checks in places where they're
needed now for shmem/tmpfs/swap.
I'll keep the bland naming, if that's okay, but send a patch adding
a line of comment in such places. Mentioning shmem, tmpfs, swap.
>
> Also, commenting out a function call might be meaningful information for
> Hugh-right-now, but for other people later on, they're just a big WTF.
Ah yes, I hadn't realized at all that those look like commented-out
function calls. No, they're comments on what the else case is that
we have arrived at there. I'll make those clearer too.
Hugh
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next prev parent reply other threads:[~2011-07-12 22:09 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 [this message]
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
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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