From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id 31DCC2C00D8 for ; Fri, 3 May 2013 18:19:19 +1000 (EST) Message-ID: <1367569143.4389.56.camel@pasglop> Subject: Re: [PATCH -V7 02/10] powerpc/THP: Implement transparent hugepages for ppc64 From: Benjamin Herrenschmidt To: David Gibson Date: Fri, 03 May 2013 18:19:03 +1000 In-Reply-To: <20130503045201.GO13041@truffula.fritz.box> References: <1367178711-8232-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <1367178711-8232-3-git-send-email-aneesh.kumar@linux.vnet.ibm.com> <20130503045201.GO13041@truffula.fritz.box> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Cc: linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, paulus@samba.org, "Aneesh Kumar K.V" List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Fri, 2013-05-03 at 14:52 +1000, David Gibson wrote: > Here, specifically, the fact that PAGE_BUSY is in PAGE_THP_HPTEFLAGS > is likely to be bad. If the page is busy, it's in the middle of > update so can't stably be considered the same as anything. _PAGE_BUSY is more like a read lock. It means it's being hashed, so what is not stable is _PAGE_HASHPTE, slot index, _ACCESSED and _DIRTY. The rest is stable and usually is what pmd_same looks at (though I have a small doubt vs. _ACCESSED and _DIRTY but at least x86 doesn't care since they are updated by HW). Cheers, Ben.