From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nick Piggin Subject: Re: Definition of x86 _PAGE_SPECIAL and sharing _PAGE_UNUSED1 Date: Thu, 28 Aug 2008 10:32:30 +1000 References: <48B5A4B0.9050308@goop.org> In-Reply-To: <48B5A4B0.9050308@goop.org> MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Content-Disposition: inline Message-Id: <200808281032.30594.nickpiggin@yahoo.com.au> Sender: owner-linux-mm@kvack.org Return-Path: To: Jeremy Fitzhardinge Cc: Ingo Molnar , Hugh Dickens , Linux Kernel Mailing List , Andrew Morton , Linux Memory Management List List-ID: On Thursday 28 August 2008 05:02, Jeremy Fitzhardinge wrote: > _PAGE_SPECIAL is overloading _PAGE_UNUSED1. Does it really leave > _PAGE_UNUSED1 available for other uses, or does it become an exclusive > user of that flag. Under what circumstances can they be shared? > > arch/x86/mm/pageattr-test.c is now using _PAGE_UNUSED1 as the flag used > to make sure that huge pages are shattered properly (previously it used > _PAGE_GLOBAL). Is that going to clash with _PAGE_SPECIAL? Ah... pity it was hidden away there and not put into the include file. > In other words, should we drop _PAGE_UNUSED1 altogether, or at least > define how the its different users can coexist? I don't feel strongly about it. But you should put your definition in pgtable.h (and possibly explain how it coexists with _SPECIAL). > Am I right in supposing that _PAGE_SPECIAL can only be set on user pages? Yes. > (Also, "SPECIAL" is awfully generic. Was there really no more > descriptive name for this?) I thought it was about on par with its counterpart, which is "normal". Either way, I don't think a casual reader would get an adequate idea of how it works in one word. normal ~= refcounted, special ~= !refcounted I guess, but it is slightly more than that and besides, normal was there first, and I think Linus coined it... if you can convince him to change it then you have my blessing to change special into whatever you want. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org