From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ross Zwisler Subject: Re: [PATCH 1/3] mm: add vm_insert_mixed_mkwrite() Date: Fri, 9 Jun 2017 21:03:46 -0600 Message-ID: <20170610030346.GA3575@linux.intel.com> References: <20170607204859.13104-1-ross.zwisler@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Ross Zwisler , Andrew Morton , Linux Kernel Mailing List , linux-xfs@vger.kernel.org, Theodore Ts'o , Matthew Wilcox , "Darrick J. Wong" , Jonathan Corbet , Steven Rostedt , linux-doc@vger.kernel.org, linux-mm , Dave Hansen , Ingo Molnar , Andreas Dilger , Alexander Viro , linux-fsdevel , Jan Kara , ext4 hackers , Christoph Hellwig , "linux-nvdimm@lists.01.org" To: Dan Williams Return-path: Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-Id: linux-ext4.vger.kernel.org On Fri, Jun 09, 2017 at 02:23:51PM -0700, Dan Williams wrote: > On Wed, Jun 7, 2017 at 1:48 PM, 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 | 9 +++++++-- > > mm/memory.c | 21 ++++++++++++++------- > > 2 files changed, 21 insertions(+), 9 deletions(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index b892e95..11e323a 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -2294,10 +2294,15 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr, > > unsigned long pfn); > > 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, bool mkwrite); > > Are there any other planned public users of vm_insert_mixed_mkwrite() > that would pass false? I think not. > > > int vm_iomap_memory(struct vm_area_struct *vma, phys_addr_t start, unsigned long len); > > > > +static inline int vm_insert_mixed(struct vm_area_struct *vma, > > + unsigned long addr, pfn_t pfn) > > +{ > > + return vm_insert_mixed_mkwrite(vma, addr, pfn, false); > > +} > > ...in other words instead of making the distinction of > vm_insert_mixed_mkwrite() and vm_insert_mixed() with extra flag > argument just move the distinction into mm/memory.c directly. > > So, the prototype remains the same as vm_insert_mixed() > > int vm_insert_mixed_mkwrite(struct vm_area_struct *vma, unsigned long > addr, pfn_t pfn); > > ...and only static insert_pfn(...) needs to change. My usage of vm_insert_mixed_mkwrite() in fs/dax.c needs the mkwrite flag to be there. From dax_insert_mapping(): return vm_insert_mixed_mkwrite(vma, vaddr, pfn, vmf->flags & FAULT_FLAG_WRITE); So, yes, we could do what you suggest, but then that code becomes: if (vmf->flags & FAULT_FLAG_WRITE) vm_insert_mixed_mkwrite(vma, vaddr, pfn); else vm_insert_mixed(vma, vaddr, pfn); And vm_insert_mixed_mkwrite() and vm_insert_mixed() are redundant with only the insert_pfn() line differing? This doesn't seem better...unless I'm missing something? The way it is, vm_insert_mixed_mkwrite() also closely matches insert_pfn_pmd(), which we use in the PMD case and which also takes a 'write' boolean which works the same as our newly added 'mkwrite'. -- 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