From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Schwidefsky Subject: Re: [PATCH 1/2] mm,thp: refactor generic deposit/withdraw routines for wider usage Date: Thu, 11 Feb 2016 12:20:23 +0100 Message-ID: <20160211122023.6d719513@mschwide> 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 Return-path: Received: from e06smtp14.uk.ibm.com ([195.75.94.110]:49200 "EHLO e06smtp14.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751140AbcBKLU3 (ORCPT ); Thu, 11 Feb 2016 06:20:29 -0500 Received: from localhost by e06smtp14.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 11 Feb 2016 11:20:28 -0000 In-Reply-To: <56BC682D.6070808@synopsys.com> Sender: linux-arch-owner@vger.kernel.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.