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From: Hugh Dickins <firstname.lastname@example.org> To: David Howells <email@example.com> Cc: Robin Holt <firstname.lastname@example.org>, "Kawai, Hidehiro" <email@example.com>, Andrew Morton <firstname.lastname@example.org>, kernel list <email@example.com>, Pavel Machek <firstname.lastname@example.org>, Alan Cox <email@example.com>, Masami Hiramatsu <firstname.lastname@example.org>, sugita <email@example.com>, Satoshi OSHIMA <firstname.lastname@example.org>, "Hideo AOKI@redhat" <email@example.com> Subject: Re: [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory Date: Mon, 5 Mar 2007 19:04:11 +0000 (GMT) [thread overview] Message-ID: <Pine.LNX.firstname.lastname@example.org> (raw) In-Reply-To: <email@example.com> On Sat, 3 Mar 2007, David Howells wrote: > Hugh Dickins <firstname.lastname@example.org> wrote: > > > > VMAs are a shared resource under NOMMU conditions. > > > > That's a disturbing remark. > > Why? No-one complained when I first put up my rewrite patches three years ago. Never mind whether anyone read your patches three years ago, it's disturbing when one body of active developers perceives an object as shared and another (largely disjoint) body of active developers perceives it as private: great scope for disaster. > > > Under precisely what NOMMU conditions? > > CONFIG_MMU=n. Believe it or not, I had just about grasped that subtlety. I was rather expecting some helpful response along the lines of "we share all the vmas across a fork" or "whenever we go to allocate a vma, we look to see if there's already an isomorphic vma which we can share" or something like that. But don't worry about it, the source is there for me to look at whenever. > > > I had thought Robin's suggestion very sensible; and throughout mm/ > > it has seemed pretty random whether we pass an "mm" argument down > > in addition to "vma", or just take vma->vm_mm at whatever level needs. > > > > You seem to be suggesting vma->vm_mm is dangerous when CONFIG_NOMMU, > > vm_mm is never set to anything other than NULL if CONFIG_MMU=n and it doesn't > seem to be a problem. I don't think anything in the mm/ directory is left that > looks at vm_mm once MMU support is disabled (in fact I've just checked, and I > can compile with vm_mm #ifdef'd out) That's reassuring, thanks. > > > but we MMU people are scarily unaware of that. > > If you're worryied that you can't compile anything for NOMMU, an FRV compiler > is available, and a suitable NOMMU default config can be provided. > Alternatively, you can pick ARM, M68K, ... > > > Perhaps you need to put #ifndef CONFIG_NOMMU around vm_mm in struct > > vm_area_struct? > > I can if it makes you happier. It's not strictly necessary, but it does make > the struct smaller which is good. No, it doesn't really make me any happier: I expect that if I look any deeper, I'll just find plenty more to worry about there. I have the impression, now reinforced by your defensive posture, that NOMMU is a hack that squeamish outsiders had better not look too deeply into: so long as it mostly works for those who need it to work, we'd probably just be wasting your time anyway. Hugh
next prev parent reply other threads:[~2007-03-05 19:04 UTC|newest] Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top 2007-02-16 13:34 [PATCH 0/4] coredump: core dump masking support v3 Kawai, Hidehiro 2007-02-16 13:39 ` [PATCH 1/4] coredump: add an interface to control the core dump routine Kawai, Hidehiro 2007-02-16 13:40 ` [PATCH 2/4] coredump: ELF: enable to omit anonymous shared memory Kawai, Hidehiro 2007-02-16 13:41 ` [PATCH 3/4] coredump: ELF-FDPIC: " Kawai, Hidehiro 2007-02-16 13:42 ` [PATCH 4/4] coredump: documentation for proc entry Kawai, Hidehiro 2007-02-16 15:05 ` [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory David Howells 2007-02-16 16:50 ` Robin Holt 2007-02-16 20:09 ` David Howells 2007-03-02 16:55 ` Hugh Dickins 2007-03-03 14:10 ` David Howells 2007-03-05 19:04 ` Hugh Dickins [this message] 2007-03-06 18:13 ` David Howells 2007-03-09 14:12 ` Move to unshared VMAs in NOMMU mode? David Howells 2007-03-12 20:50 ` Robin Getz 2007-03-13 10:14 ` David Howells 2007-03-15 21:20 ` Hugh Dickins 2007-03-15 22:47 ` David Howells 2007-03-19 19:23 ` Eric W. Biederman 2007-03-20 11:06 ` David Howells 2007-03-20 16:48 ` Eric W. Biederman 2007-03-20 19:12 ` David Howells 2007-03-20 19:51 ` David Howells 2007-03-21 16:11 ` David Howells 2007-03-03 14:25 ` [PATCH] NOMMU: Hide vm_mm in NOMMU mode David Howells 2007-02-20 9:45 ` [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory Kawai, Hidehiro 2007-02-20 10:58 ` David Howells 2007-02-20 12:56 ` Robin Holt 2007-02-21 10:00 ` Kawai, Hidehiro 2007-02-21 11:33 ` David Howells 2007-02-21 11:54 ` Robin Holt 2007-02-22 5:33 ` Kawai, Hidehiro 2007-02-22 11:47 ` David Howells 2007-02-16 15:08 ` [PATCH 0/4] coredump: core dump masking support v3 David Howells 2007-02-20 9:48 ` Kawai, Hidehiro 2007-02-24 3:32 ` Markus Gutschke 2007-02-24 11:39 ` Pavel Machek 2007-03-01 12:35 ` Kawai, Hidehiro 2007-03-01 18:16 ` Markus Gutschke 2007-02-24 10:02 ` David Howells 2007-02-24 20:01 ` Markus Gutschke 2007-02-26 11:49 ` David Howells 2007-02-26 12:01 ` Pavel Machek 2007-02-26 12:42 ` David Howells 2007-03-02 4:41 [PATCH 0/4] coredump: core dump masking support v4 Kawai, Hidehiro 2007-03-02 4:50 ` [PATCH 3/4] coredump: ELF-FDPIC: enable to omit anonymous shared memory Kawai, Hidehiro
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