Messages in this thread | | | Subject | Re: [PATCH] Define a UNIQUE value for AS_UNEVICTABLE flag | From | Lee Schermerhorn <> | Date | Thu, 02 Apr 2009 14:08:45 -0400 |
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On Thu, 2009-04-02 at 09:53 -0700, Andrew Morton wrote: > On Thu, 02 Apr 2009 12:47:15 -0400 Lee Schermerhorn <Lee.Schermerhorn@hp.com> wrote: > > > [PATCH] Define UNIQUE value of AS_UNEVICTABLE > > > > Needed in 2.6.28, 2.6.29, ... > > > > A new "address_space flag"--AS_MM_ALL_LOCKS--was defined to use the next > > available AS flag while the Unevictable LRU was under development. The > > Unevictable LRU was using the same flag and "no one" noticed. Current > > mainline, since 2.6.28, has same value for two symbolic flag names. > > argh. > > What are the user-observable effects of the bug, and why didn't anyone > notice it until now?
Well, AS_MM_ALL_LOCKS seems to be used for mmu notifiers. So, I expect I've never enabled it. However, I think that if it got set, all of the pages in all of the vmas that had it set will appear to be unevictable. This would only matter if/when one tried to reclaim/evict them. The pages would probably get stranded on the unevictable lru [until freed] in that case as there would be no scan to rescue them when AS_MM_ALL_LOCKS is cleared.
Not sure about the other way around: flag set as AS_UNEVICTABLE and code examining AS_MM_ALL_LOCKS sees it...
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