From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f43.google.com (mail-wm0-f43.google.com [74.125.82.43]) by kanga.kvack.org (Postfix) with ESMTP id 648B56B0009 for ; Thu, 11 Feb 2016 06:20:29 -0500 (EST) Received: by mail-wm0-f43.google.com with SMTP id g62so16676020wme.0 for ; Thu, 11 Feb 2016 03:20:29 -0800 (PST) Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com. [195.75.94.106]) by mx.google.com with ESMTPS id 1si12194286wmy.90.2016.02.11.03.20.28 for (version=TLS1 cipher=AES128-SHA bits=128/128); Thu, 11 Feb 2016 03:20:28 -0800 (PST) Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 11 Feb 2016 11:20:27 -0000 Received: from b06cxnps4075.portsmouth.uk.ibm.com (d06relay12.portsmouth.uk.ibm.com [9.149.109.197]) by d06dlp02.portsmouth.uk.ibm.com (Postfix) with ESMTP id C98D62190023 for ; Thu, 11 Feb 2016 11:20:10 +0000 (GMT) Received: from d06av07.portsmouth.uk.ibm.com (d06av07.portsmouth.uk.ibm.com [9.149.37.248]) by b06cxnps4075.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u1BBKPQM15990944 for ; Thu, 11 Feb 2016 11:20:25 GMT Received: from d06av07.portsmouth.uk.ibm.com (localhost [127.0.0.1]) by d06av07.portsmouth.uk.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u1BBKOMf007131 for ; Thu, 11 Feb 2016 06:20:24 -0500 Date: Thu, 11 Feb 2016 12:20:23 +0100 From: Martin Schwidefsky Subject: Re: [PATCH 1/2] mm,thp: refactor generic deposit/withdraw routines for wider usage Message-ID: <20160211122023.6d719513@mschwide> In-Reply-To: <56BC682D.6070808@synopsys.com> References: <1455182907-15445-1-git-send-email-vgupta@synopsys.com> <1455182907-15445-2-git-send-email-vgupta@synopsys.com> <20160211112223.0acc8237@mschwide> <56BC682D.6070808@synopsys.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Vineet Gupta Cc: Andrew Morton , "Kirill A. Shutemov" , "Aneesh Kumar K.V" , "David S. Miller" , Alex Thorlton , Gerald Schaefer , linux-snps-arc@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, Andrea Arcangeli On Thu, 11 Feb 2016 16:23:33 +0530 Vineet Gupta wrote: > On Thursday 11 February 2016 03:52 PM, Martin Schwidefsky wrote: > > On Thu, 11 Feb 2016 14:58:26 +0530 > > Vineet Gupta wrote: > > > >> Generic pgtable_trans_huge_deposit()/pgtable_trans_huge_withdraw() > >> assume pgtable_t to be struct page * which is not true for all arches. > >> Thus arc, s390, sparch end up with their own copies despite no special > >> hardware requirements (unlike powerpc). > > > > s390 does have a special hardware requirement. pgtable_t is an address > > for a 2K block of memory. It is *not* equivalent to a struct page * > > which refers to a 4K block of memory. That has been the whole point > > to introduce pgtable_t. > > Actually my reference to hardware requirement was more like powerpc style save a > hash value some where etc. > > Now pgtable_t need not be struct page * even if the actual sizes are same - e.g. > in ARC port I kept pgtable_t as pte_t * simply to avoid a few page_address() calls > in mm code (you could argue that is was a micro-optimization, anyways..) > > So given I know nothing about s390 MMU internals, I still think you can switch to > the update generic version despite 2K vs. 4K. Agree ? No, we can not. For s390 a page table is aligned on a 2K boundary and is only half the size of a page (except for KVM but that is another story). For s390 a pgtable_t is a pointer to the memory location with the 256 ptes and not a struct page *. The cast "struct page *new = (struct page*)pgtable;" in your first patch is already broken, "new" points to the memory of the page table and the list_head operations will clobber that memory. You try to fix it up with the memset to zero in pgtable_trans_huge_withdraw but that does not correct the pte entries for s390 as an invalid page-table entry is *not* all zeros. In short, please let s390 keep its own copy of deposit/withdraw. -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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