From: Andrew Morton <akpm@linux-foundation.org>
To: Rich Felker <dalias@libc.org>
Cc: linux-kernel@vger.kernel.org, Michal Hocko <mhocko@suse.com>,
Greg Ungerer <gerg@uclinux.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Yoshinori Sato <ysato@users.sourceforge.jp>
Subject: Re: [PATCH] tmpfs: fix VM_MAYSHARE mappings for NOMMU
Date: Mon, 25 Apr 2016 17:09:09 -0700 [thread overview]
Message-ID: <20160425170909.31cf27c845a9fc19688fd5af@linux-foundation.org> (raw)
In-Reply-To: <20160422221944.GA14264@brightrain.aerifal.cx>
On Fri, 22 Apr 2016 18:19:44 -0400 Rich Felker <dalias@libc.org> wrote:
> Subject: [PATCH] tmpfs: fix VM_MAYSHARE mappings for NOMMU
I take it that "ramfs" was intended here.
> The nommu do_mmap expects f_op->get_unmapped_area to either succeed or
> return -ENOSYS for VM_MAYSHARE (e.g. private read-only) mappings.
> Returning addr in the non-MAP_SHARED case was completely wrong, and
> only happened to work because addr was 0. However, it prevented
> VM_MAYSHARE mappings from sharing backing with the fs cache, and
> forced such mappings (including shareable program text) to be copied
> whenever the number of mappings transitioned from 0 to 1, impacting
> performance and memory usage. Subsequent mappings beyond the first
> still correctly shared memory with the first.
>
> Instead, treat VM_MAYSHARE identically to VM_SHARED at the file ops
> level; do_mmap already handles the semantic differences between them.
>
> ...
>
next prev parent reply other threads:[~2016-04-26 0:09 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-04-22 22:19 Rich Felker
2016-04-26 0:09 ` Andrew Morton [this message]
2016-04-26 0:41 ` Rich Felker
2016-04-26 0:47 ` Rich Felker
2016-04-26 2:40 ` Andrew Morton
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