On Fri, Aug 23, 2019 at 11:18:26AM -0400, Vivek Goyal wrote: > On Fri, Aug 09, 2019 at 03:58:20PM -0700, ira.weiny@xxxxxxxxx wrote: > > From: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > Callers of dax_layout_busy_page() are only rarely operating on the > > entire file of concern. > > > > Teach dax_layout_busy_page() to operate on a sub-range of the > > address_space provided. Specifying 0 - ULONG_MAX however, will continue > > to operate on the "entire file" and XFS is split out to a separate patch > > by this method. > > > > This could potentially speed up dax_layout_busy_page() as well. > > I need this functionality as well for virtio_fs and posted a patch for > this. > > https://lkml.org/lkml/2019/8/21/825 > > Given this is an optimization which existing users can benefit from already, > this patch could probably be pushed upstream independently. I'm ok with that. However, this patch does not apply cleanly to head as I had some other additions to dax.h. > > > > > Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx> > > > > --- > > Changes from RFC v1 > > Fix 0-day build errors > > > > fs/dax.c | 15 +++++++++++---- > > fs/ext4/ext4.h | 2 +- > > fs/ext4/extents.c | 6 +++--- > > fs/ext4/inode.c | 19 ++++++++++++------- > > fs/xfs/xfs_file.c | 3 ++- > > include/linux/dax.h | 6 ++++-- > > 6 files changed, 33 insertions(+), 18 deletions(-) > > > > diff --git a/fs/dax.c b/fs/dax.c > > index a14ec32255d8..3ad19c384454 100644 > > --- a/fs/dax.c > > +++ b/fs/dax.c > > @@ -573,8 +573,11 @@ bool dax_mapping_is_dax(struct address_space *mapping) > > EXPORT_SYMBOL_GPL(dax_mapping_is_dax); > > > > /** > > - * dax_layout_busy_page - find first pinned page in @mapping > > + * dax_layout_busy_page - find first pinned page in @mapping within > > + * the range @off - @off + @len > > * @mapping: address space to scan for a page with ref count > 1 > > + * @off: offset to start at > > + * @len: length to scan through > > * > > * DAX requires ZONE_DEVICE mapped pages. These pages are never > > * 'onlined' to the page allocator so they are considered idle when > > @@ -587,9 +590,13 @@ EXPORT_SYMBOL_GPL(dax_mapping_is_dax); > > * to be able to run unmap_mapping_range() and subsequently not race > > * mapping_mapped() becoming true. > > */ > > -struct page *dax_layout_busy_page(struct address_space *mapping) > > +struct page *dax_layout_busy_page(struct address_space *mapping, > > + loff_t off, loff_t len) > > { > > - XA_STATE(xas, &mapping->i_pages, 0); > > + unsigned long start_idx = off >> PAGE_SHIFT; > > + unsigned long end_idx = (len == ULONG_MAX) ? ULONG_MAX > > + : start_idx + (len >> PAGE_SHIFT); > > + XA_STATE(xas, &mapping->i_pages, start_idx); > > void *entry; > > unsigned int scanned = 0; > > struct page *page = NULL; > > @@ -612,7 +619,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping) > > unmap_mapping_range(mapping, 0, 0, 1); > > Should we unmap only those pages which fall in the range specified by caller. > Unmapping whole file seems to be less efficient. Seems reasonable to me. I was focused on getting pages which were busy not necessarily on what got unmapped. So I did not consider this. Thanks for the suggestion. However, I don't understand the math you do for length? Is this comment/code correct? + /* length is being calculated from lstart and not start. + * This is due to behavior of unmap_mapping_range(). If + * start is say 4094 and end is on 4093 then want to + * unamp two pages, idx 0 and 1. But unmap_mapping_range() + * will unmap only page at idx 0. If we calculate len + * from the rounded down start, this problem should not + * happen. + */ + len = end - lstart + 1; How can end (4093) be < start (4094)? Is that valid? And why would a start of 4094 unmap idx 0? Ira
