| Message ID | 20170824152207.30729-3-hch@lst.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Aug 24, 2017 at 05:22:06PM +0200, Christoph Hellwig wrote: > Add a new __xfs_filemap_fault helper that implements all four page fault > callouts, and make these methods themselves small stubs that set the > correct write_fault flag, and exit early for the non-DAX case for the > hugepage related ones. > > Life would be so much simpler if we only had one method for all this. > > Signed-off-by: Christoph Hellwig <hch@lst.de> A few nits and a question below. This looks much simpler and gets rid of a lot of duplication. Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com> <> > STATIC int > xfs_filemap_huge_fault( > struct vm_fault *vmf, > enum page_entry_size pe_size) > { > - struct inode *inode = file_inode(vmf->vma->vm_file); > - struct xfs_inode *ip = XFS_I(inode); > - int ret; > - > - if (!IS_DAX(inode)) > + if (!IS_DAX(file_inode(vmf->vma->vm_file))) > return VM_FAULT_FALLBACK; > > - trace_xfs_filemap_huge_fault(ip); > - > - if (vmf->flags & FAULT_FLAG_WRITE) { > - sb_start_pagefault(inode->i_sb); > - file_update_time(vmf->vma->vm_file); > - } > - > - xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED); > - ret = dax_iomap_fault(vmf, pe_size, NULL, &xfs_iomap_ops); > - xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED); > - > - if (vmf->flags & FAULT_FLAG_WRITE) > - sb_end_pagefault(inode->i_sb); > + /* DAX can shortcut the normal fault path on write faults! */ Does this comment still make sense for the PMD case? Here's what I *think* it means: For DAX write faults we make the PTE writeable in the ->fault() code and don't rely on a follow-up ->page_mkwrite() call. This happens in do_shared_fault(), where we return before the ->page_mkwrite() call because the DAX write fault returns VM_FAULT_NOPAGE. This is in contrast to the normal page fault case where the ->fault() call ends up calling filemap_fault(), which populates the page read-only, and then do_shared_fault() does a follow-up ->page_mkwrite() call which makes the page writable. First, is the above correct? :) If so, I think the comment doesn't make sense for the PMD fault path because in that case we always make the PMD writeable in the first ->huge_fault() call, as there is no follow-up *_mkwrite()? > + return __xfs_filemap_fault(vmf, pe_size, > + (vmf->flags & FAULT_FLAG_WRITE)); > +} > > - return ret; > +STATIC int > +xfs_filemap_page_mkwrite( > + struct vm_fault *vmf) > +{ > + return __xfs_filemap_fault(vmf, PE_SIZE_PTE, true); > } > > -/* > - * pfn_mkwrite was originally inteneded to ensure we capture time stamp > - * updates on write faults. In reality, it's need to serialise against > - * truncate similar to page_mkwrite. Hence we cycle the XFS_MMAPLOCK_SHARED > - * to ensure we serialise the fault barrier in place. > - */ > static int STATIC > xfs_filemap_pfn_mkwrite( > struct vm_fault *vmf) > { > - > - struct inode *inode = file_inode(vmf->vma->vm_file); > - struct xfs_inode *ip = XFS_I(inode); > - int ret = VM_FAULT_NOPAGE; > - loff_t size; > - > - trace_xfs_filemap_pfn_mkwrite(ip); > - > - sb_start_pagefault(inode->i_sb); > - file_update_time(vmf->vma->vm_file); > - > - /* check if the faulting page hasn't raced with truncate */ > - xfs_ilock(ip, XFS_MMAPLOCK_SHARED); > - size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; I see that this size check is gone from the new code, and we now rely on the equivalent check in dax_iomap_fault(). Nice. > - if (vmf->pgoff >= size) > - ret = VM_FAULT_SIGBUS; > - else if (IS_DAX(inode)) > - ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, &xfs_iomap_ops); > - xfs_iunlock(ip, XFS_MMAPLOCK_SHARED); > - sb_end_pagefault(inode->i_sb); > - return ret; > - > + if (!IS_DAX(file_inode(vmf->vma->vm_file))) > + return VM_FAULT_NOPAGE; > + return __xfs_filemap_fault(vmf, PE_SIZE_PTE, true); > } > > static const struct vm_operations_struct xfs_file_vm_ops = { > diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h > index bcc3cdf8e1c5..3f41d5340eb8 100644 > --- a/fs/xfs/xfs_trace.h > +++ b/fs/xfs/xfs_trace.h > @@ -689,10 +689,26 @@ DEFINE_INODE_EVENT(xfs_inode_set_cowblocks_tag); > DEFINE_INODE_EVENT(xfs_inode_clear_cowblocks_tag); > DEFINE_INODE_EVENT(xfs_inode_free_cowblocks_invalid); > > -DEFINE_INODE_EVENT(xfs_filemap_fault); > -DEFINE_INODE_EVENT(xfs_filemap_huge_fault); > -DEFINE_INODE_EVENT(xfs_filemap_page_mkwrite); > -DEFINE_INODE_EVENT(xfs_filemap_pfn_mkwrite); > +TRACE_EVENT(xfs_filemap_fault, > + TP_PROTO(struct xfs_inode *ip, enum page_entry_size pe_size, > + bool write_fault), > + TP_ARGS(ip, pe_size, write_fault), > + TP_STRUCT__entry( > + __field(dev_t, dev) > + __field(xfs_ino_t, ino) > + __field(enum page_entry_size, pe_size) > + __field(bool, write_fault) > + ), > + TP_fast_assign( > + __entry->dev = VFS_I(ip)->i_sb->s_dev; > + __entry->ino = ip->i_ino; > + __entry->pe_size = pe_size; > + __entry->write_fault = write_fault; > + ), > + TP_printk("dev %d:%d ino 0x%llx pe_size %d write_fault %d", > + MAJOR(__entry->dev), MINOR(__entry->dev), > + __entry->ino, __entry->pe_size, __entry->write_fault) > +) I wonder if pe_size would be more readable as a string via __print_symbolic() so we see "pe_size PMD" instead of "pe_size 1" from enum page_entry_size?
On Thu, Aug 24, 2017 at 03:29:42PM -0600, Ross Zwisler wrote: > > + /* DAX can shortcut the normal fault path on write faults! */ > > Does this comment still make sense for the PMD case? I kept the code as before, and also kept the comment intent as-is (although I shortend it a bit). > Here's what I *think* it > means: For DAX write faults we make the PTE writeable in the ->fault() code > and don't rely on a follow-up ->page_mkwrite() call. This happens in > do_shared_fault(), where we return before the ->page_mkwrite() call because > the DAX write fault returns VM_FAULT_NOPAGE. > > This is in contrast to the normal page fault case where the ->fault() call > ends up calling filemap_fault(), which populates the page read-only, and then > do_shared_fault() does a follow-up ->page_mkwrite() call which makes the page > writable. > > First, is the above correct? :) Yes. > If so, I think the comment doesn't make > sense for the PMD fault path because in that case we always make the PMD > writeable in the first ->huge_fault() call, as there is no follow-up > *_mkwrite()? Well, there is non-DAX huge_fault case. It still is different from the normal non-hugepage fault case, so the comment still makes some sense, but maybe I should remove the DAX. That being said if we eventually get huge page page cache support (patches are on the list) I suspect they'll work like the normal fault path, not the DAX path. > > static int > > STATIC We're phasing that out, so I should probably remove it where it's currently newly added/moved in the patch. > I see that this size check is gone from the new code, and we now rely on the > equivalent check in dax_iomap_fault(). Nice. Yes. And I actually used to mention that in the changelog, but it got lost. I'll re-add it. > I wonder if pe_size would be more readable as a string via __print_symbolic() > so we see "pe_size PMD" instead of "pe_size 1" from enum page_entry_size? Probably. I was just lazy :) If I want to go all the way I could also use a __print_flags for the FAULT_FLAG_* flags.
On Fri, Aug 25, 2017 at 09:15:38AM +0200, Christoph Hellwig wrote: > On Thu, Aug 24, 2017 at 03:29:42PM -0600, Ross Zwisler wrote: <> > > I wonder if pe_size would be more readable as a string via __print_symbolic() > > so we see "pe_size PMD" instead of "pe_size 1" from enum page_entry_size? > > Probably. I was just lazy :) If I want to go all the way I could also > use a __print_flags for the FAULT_FLAG_* flags. Yep - I'm doing that in include/trace/events/fs_dax.h if you want to just copy & paste.
On Mon, Aug 28, 2017 at 11:50:14AM -0600, Ross Zwisler wrote: > Yep - I'm doing that in include/trace/events/fs_dax.h if you want to just copy > & paste. Oh, nice. But maybe we need the trace point in the core MM instead of in XFS and the DAX code? :)
On Mon, Aug 28, 2017 at 07:52:57PM +0200, Christoph Hellwig wrote: > On Mon, Aug 28, 2017 at 11:50:14AM -0600, Ross Zwisler wrote: > > Yep - I'm doing that in include/trace/events/fs_dax.h if you want to just copy > > & paste. > > Oh, nice. But maybe we need the trace point in the core MM instead > of in XFS and the DAX code? :) Yea, there aren't any tracepoints at all in mm/memory.c. I'm not sure if that's because we just haven't gotten around to putting them in, or if for some reason it was intentional to not trace that bit of code?
diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c index 4213f02325a2..460ca9639e66 100644 --- a/fs/xfs/xfs_file.c +++ b/fs/xfs/xfs_file.c @@ -1012,34 +1012,36 @@ xfs_file_llseek( * i_lock (XFS - extent map serialisation) */ -/* - * mmap()d file has taken write protection fault and is being made writable. We - * can set the page state up correctly for a writable page, which means we can - * do correct delalloc accounting (ENOSPC checking!) and unwritten extent - * mapping. - */ STATIC int -xfs_filemap_page_mkwrite( - struct vm_fault *vmf) +__xfs_filemap_fault( + struct vm_fault *vmf, + enum page_entry_size pe_size, + bool write_fault) { struct inode *inode = file_inode(vmf->vma->vm_file); + struct xfs_inode *ip = XFS_I(inode); int ret; - trace_xfs_filemap_page_mkwrite(XFS_I(inode)); + trace_xfs_filemap_fault(ip, pe_size, write_fault); - sb_start_pagefault(inode->i_sb); - file_update_time(vmf->vma->vm_file); - xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED); + if (write_fault) { + sb_start_pagefault(inode->i_sb); + file_update_time(vmf->vma->vm_file); + } + xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED); if (IS_DAX(inode)) { - ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, &xfs_iomap_ops); + ret = dax_iomap_fault(vmf, pe_size, NULL, &xfs_iomap_ops); } else { - ret = iomap_page_mkwrite(vmf, &xfs_iomap_ops); + if (write_fault) + ret = iomap_page_mkwrite(vmf, &xfs_iomap_ops); + else + ret = filemap_fault(vmf); } - xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED); - sb_end_pagefault(inode->i_sb); + if (write_fault) + sb_end_pagefault(inode->i_sb); return ret; } @@ -1047,93 +1049,39 @@ STATIC int xfs_filemap_fault( struct vm_fault *vmf) { - struct inode *inode = file_inode(vmf->vma->vm_file); - int ret; - - trace_xfs_filemap_fault(XFS_I(inode)); - /* DAX can shortcut the normal fault path on write faults! */ - if ((vmf->flags & FAULT_FLAG_WRITE) && IS_DAX(inode)) - return xfs_filemap_page_mkwrite(vmf); - - xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED); - if (IS_DAX(inode)) - ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, &xfs_iomap_ops); - else - ret = filemap_fault(vmf); - xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED); - - return ret; + return __xfs_filemap_fault(vmf, PE_SIZE_PTE, + IS_DAX(file_inode(vmf->vma->vm_file)) && + (vmf->flags & FAULT_FLAG_WRITE)); } -/* - * Similar to xfs_filemap_fault(), the DAX fault path can call into here on - * both read and write faults. Hence we need to handle both cases. There is no - * ->huge_mkwrite callout for huge pages, so we have a single function here to - * handle both cases here. @flags carries the information on the type of fault - * occuring. - */ STATIC int xfs_filemap_huge_fault( struct vm_fault *vmf, enum page_entry_size pe_size) { - struct inode *inode = file_inode(vmf->vma->vm_file); - struct xfs_inode *ip = XFS_I(inode); - int ret; - - if (!IS_DAX(inode)) + if (!IS_DAX(file_inode(vmf->vma->vm_file))) return VM_FAULT_FALLBACK; - trace_xfs_filemap_huge_fault(ip); - - if (vmf->flags & FAULT_FLAG_WRITE) { - sb_start_pagefault(inode->i_sb); - file_update_time(vmf->vma->vm_file); - } - - xfs_ilock(XFS_I(inode), XFS_MMAPLOCK_SHARED); - ret = dax_iomap_fault(vmf, pe_size, NULL, &xfs_iomap_ops); - xfs_iunlock(XFS_I(inode), XFS_MMAPLOCK_SHARED); - - if (vmf->flags & FAULT_FLAG_WRITE) - sb_end_pagefault(inode->i_sb); + /* DAX can shortcut the normal fault path on write faults! */ + return __xfs_filemap_fault(vmf, pe_size, + (vmf->flags & FAULT_FLAG_WRITE)); +} - return ret; +STATIC int +xfs_filemap_page_mkwrite( + struct vm_fault *vmf) +{ + return __xfs_filemap_fault(vmf, PE_SIZE_PTE, true); } -/* - * pfn_mkwrite was originally inteneded to ensure we capture time stamp - * updates on write faults. In reality, it's need to serialise against - * truncate similar to page_mkwrite. Hence we cycle the XFS_MMAPLOCK_SHARED - * to ensure we serialise the fault barrier in place. - */ static int xfs_filemap_pfn_mkwrite( struct vm_fault *vmf) { - - struct inode *inode = file_inode(vmf->vma->vm_file); - struct xfs_inode *ip = XFS_I(inode); - int ret = VM_FAULT_NOPAGE; - loff_t size; - - trace_xfs_filemap_pfn_mkwrite(ip); - - sb_start_pagefault(inode->i_sb); - file_update_time(vmf->vma->vm_file); - - /* check if the faulting page hasn't raced with truncate */ - xfs_ilock(ip, XFS_MMAPLOCK_SHARED); - size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT; - if (vmf->pgoff >= size) - ret = VM_FAULT_SIGBUS; - else if (IS_DAX(inode)) - ret = dax_iomap_fault(vmf, PE_SIZE_PTE, NULL, &xfs_iomap_ops); - xfs_iunlock(ip, XFS_MMAPLOCK_SHARED); - sb_end_pagefault(inode->i_sb); - return ret; - + if (!IS_DAX(file_inode(vmf->vma->vm_file))) + return VM_FAULT_NOPAGE; + return __xfs_filemap_fault(vmf, PE_SIZE_PTE, true); } static const struct vm_operations_struct xfs_file_vm_ops = { diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h index bcc3cdf8e1c5..3f41d5340eb8 100644 --- a/fs/xfs/xfs_trace.h +++ b/fs/xfs/xfs_trace.h @@ -689,10 +689,26 @@ DEFINE_INODE_EVENT(xfs_inode_set_cowblocks_tag); DEFINE_INODE_EVENT(xfs_inode_clear_cowblocks_tag); DEFINE_INODE_EVENT(xfs_inode_free_cowblocks_invalid); -DEFINE_INODE_EVENT(xfs_filemap_fault); -DEFINE_INODE_EVENT(xfs_filemap_huge_fault); -DEFINE_INODE_EVENT(xfs_filemap_page_mkwrite); -DEFINE_INODE_EVENT(xfs_filemap_pfn_mkwrite); +TRACE_EVENT(xfs_filemap_fault, + TP_PROTO(struct xfs_inode *ip, enum page_entry_size pe_size, + bool write_fault), + TP_ARGS(ip, pe_size, write_fault), + TP_STRUCT__entry( + __field(dev_t, dev) + __field(xfs_ino_t, ino) + __field(enum page_entry_size, pe_size) + __field(bool, write_fault) + ), + TP_fast_assign( + __entry->dev = VFS_I(ip)->i_sb->s_dev; + __entry->ino = ip->i_ino; + __entry->pe_size = pe_size; + __entry->write_fault = write_fault; + ), + TP_printk("dev %d:%d ino 0x%llx pe_size %d write_fault %d", + MAJOR(__entry->dev), MINOR(__entry->dev), + __entry->ino, __entry->pe_size, __entry->write_fault) +) DECLARE_EVENT_CLASS(xfs_iref_class, TP_PROTO(struct xfs_inode *ip, unsigned long caller_ip),
Add a new __xfs_filemap_fault helper that implements all four page fault callouts, and make these methods themselves small stubs that set the correct write_fault flag, and exit early for the non-DAX case for the hugepage related ones. Life would be so much simpler if we only had one method for all this. Signed-off-by: Christoph Hellwig <hch@lst.de> --- fs/xfs/xfs_file.c | 120 +++++++++++++++-------------------------------------- fs/xfs/xfs_trace.h | 24 +++++++++-- 2 files changed, 54 insertions(+), 90 deletions(-)