From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965502AbdGTP0W (ORCPT ); Thu, 20 Jul 2017 11:26:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:19888 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965003AbdGTP0T (ORCPT ); Thu, 20 Jul 2017 11:26:19 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 5D4DD796FA Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx01.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=vgoyal@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 5D4DD796FA Date: Thu, 20 Jul 2017 11:26:16 -0400 From: Vivek Goyal To: Ross Zwisler Cc: Andrew Morton , linux-kernel@vger.kernel.org, "Darrick J. Wong" , "Theodore Ts'o" , Alexander Viro , Andreas Dilger , Christoph Hellwig , Dan Williams , Dave Hansen , Ingo Molnar , Jan Kara , Jonathan Corbet , Matthew Wilcox , Steven Rostedt , linux-doc@vger.kernel.org, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-nvdimm@lists.01.org, linux-xfs@vger.kernel.org Subject: Re: [PATCH v3 1/5] mm: add vm_insert_mixed_mkwrite() Message-ID: <20170720152616.GB6664@redhat.com> References: <20170628220152.28161-1-ross.zwisler@linux.intel.com> <20170628220152.28161-2-ross.zwisler@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170628220152.28161-2-ross.zwisler@linux.intel.com> User-Agent: Mutt/1.7.1 (2016-10-04) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Thu, 20 Jul 2017 15:26:18 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 28, 2017 at 04:01:48PM -0600, Ross Zwisler wrote: > To be able to use the common 4k zero page in DAX we need to have our PTE > fault path look more like our PMD fault path where a PTE entry can be > marked as dirty and writeable as it is first inserted, rather than waiting > for a follow-up dax_pfn_mkwrite() => finish_mkwrite_fault() call. > > Right now we can rely on having a dax_pfn_mkwrite() call because we can > distinguish between these two cases in do_wp_page(): > > case 1: 4k zero page => writable DAX storage > case 2: read-only DAX storage => writeable DAX storage > > This distinction is made by via vm_normal_page(). vm_normal_page() returns > false for the common 4k zero page, though, just as it does for DAX ptes. > Instead of special casing the DAX + 4k zero page case, we will simplify our > DAX PTE page fault sequence so that it matches our DAX PMD sequence, and > get rid of dax_pfn_mkwrite() completely. > > This means that insert_pfn() needs to follow the lead of insert_pfn_pmd() > and allow us to pass in a 'mkwrite' flag. If 'mkwrite' is set insert_pfn() > will do the work that was previously done by wp_page_reuse() as part of the > dax_pfn_mkwrite() call path. > > Signed-off-by: Ross Zwisler > --- > include/linux/mm.h | 2 ++ > mm/memory.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++----- > 2 files changed, 54 insertions(+), 5 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 6f543a4..096052f 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -2293,6 +2293,8 @@ int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > unsigned long pfn, pgprot_t pgprot); > int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, > pfn_t pfn); > +int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr, > + pfn_t pfn); > int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len); > > > diff --git a/mm/memory.c b/mm/memory.c > index bb11c47..de4aa71 100644 > --- a/mm/memory.c > +++ b/mm/memory.c > @@ -1646,7 +1646,7 @@ int vm_insert_page(struct vm_area_struct *vma, unsigned long addr, > EXPORT_SYMBOL(vm_insert_page); > > static int insert_pfn(struct vm_area_struct *vma, unsigned long addr, > - pfn_t pfn, pgprot_t prot) > + pfn_t pfn, pgprot_t prot, bool mkwrite) > { > struct mm_struct *mm = vma->vm_mm; > int retval; > @@ -1658,14 +1658,26 @@ static int insert_pfn(struct vm_area_struct *vma, unsigned long addr, > if (!pte) > goto out; > retval = -EBUSY; > - if (!pte_none(*pte)) > - goto out_unlock; > + if (!pte_none(*pte)) { > + if (mkwrite) { > + entry = *pte; > + goto out_mkwrite; > + } else > + goto out_unlock; > + } > > /* Ok, finally just insert the thing.. */ > if (pfn_t_devmap(pfn)) > entry = pte_mkdevmap(pfn_t_pte(pfn, prot)); > else > entry = pte_mkspecial(pfn_t_pte(pfn, prot)); > + > +out_mkwrite: > + if (mkwrite) { > + entry = pte_mkyoung(entry); > + entry = maybe_mkwrite(pte_mkdirty(entry), vma); > + } > + > set_pte_at(mm, addr, pte, entry); > update_mmu_cache(vma, addr, pte); /* XXX: why not for insert_page? */ > > @@ -1736,7 +1748,8 @@ int vm_insert_pfn_prot(struct vm_area_struct *vma, unsigned long addr, > > track_pfn_insert(vma, &pgprot, __pfn_to_pfn_t(pfn, PFN_DEV)); > > - ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot); > + ret = insert_pfn(vma, addr, __pfn_to_pfn_t(pfn, PFN_DEV), pgprot, > + false); > > return ret; > } > @@ -1772,10 +1785,44 @@ int vm_insert_mixed(struct vm_area_struct *vma, unsigned long addr, > page = pfn_to_page(pfn_t_to_pfn(pfn)); > return insert_page(vma, addr, page, pgprot); > } > - return insert_pfn(vma, addr, pfn, pgprot); > + return insert_pfn(vma, addr, pfn, pgprot, false); > } > EXPORT_SYMBOL(vm_insert_mixed); > > +int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long addr, > + pfn_t pfn) > +{ > + pgprot_t pgprot = vma->vm_page_prot; > + > + BUG_ON(!(vma->vm_flags & VM_MIXEDMAP)); > + > + if (addr < vma->vm_start || addr >= vma->vm_end) > + return -EFAULT; > + > + track_pfn_insert(vma, &pgprot, pfn); > + > + /* > + * If we don't have pte special, then we have to use the pfn_valid() > + * based VM_MIXEDMAP scheme (see vm_normal_page), and thus we *must* > + * refcount the page if pfn_valid is true (hence insert_page rather > + * than insert_pfn). If a zero_pfn were inserted into a VM_MIXEDMAP > + * without pte special, it would there be refcounted as a normal page. > + */ > + if (!HAVE_PTE_SPECIAL && !pfn_t_devmap(pfn) && pfn_t_valid(pfn)) { > + struct page *page; > + > + /* > + * At this point we are committed to insert_page() > + * regardless of whether the caller specified flags that > + * result in pfn_t_has_page() == false. > + */ > + page = pfn_to_page(pfn_t_to_pfn(pfn)); > + return insert_page(vma, addr, page, pgprot); > + } > + return insert_pfn(vma, addr, pfn, pgprot, true); > +} > +EXPORT_SYMBOL(vm_insert_mixed_mkwrite); Hi Ross, vm_insert_mixed_mkwrite() is same as vm_insert_mixed() except this sets write parameter to inser_pfn() true. Will it make sense to just add mkwrite parameter to vm_insert_mixed() and not add a new helper function. (like insert_pfn()). Vivek