[PATCH 4/7] xfs: teach xfile to pass back direct-map pages to caller

Darrick J. Wong
2023-07-27T22:26:25Z

Certain xfile array operations (such as sorting) can be sped up quite a
bit by allowing xfile users to grab a page to bulk-read the records
contained within it. Create helper methods to facilitate this.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Kent Overstreet <kent.overstreet@linux.dev>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/scrub/trace.h | 2 +
fs/xfs/scrub/xfile.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/scrub/xfile.h | 10 +++++
3 files changed, 120 insertions(+)

diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index 1c9a31dc4e223..f8c814e07587f 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -821,6 +821,8 @@ DEFINE_EVENT(xfile_class, name, \
DEFINE_XFILE_EVENT(xfile_pread);
DEFINE_XFILE_EVENT(xfile_pwrite);
DEFINE_XFILE_EVENT(xfile_seek_data);
+DEFINE_XFILE_EVENT(xfile_get_page);
+DEFINE_XFILE_EVENT(xfile_put_page);

TRACE_EVENT(xfarray_create,
TP_PROTO(struct xfarray *xfa, unsigned long long required_capacity),
diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
index 19d512887980f..d98e8e77c684f 100644
--- a/fs/xfs/scrub/xfile.c
+++ b/fs/xfs/scrub/xfile.c
@@ -310,3 +310,111 @@ xfile_stat(
statbuf->bytes = ks.blocks << SECTOR_SHIFT;
return 0;
}
+
+/*
+ * Grab the (locked) page for a memory object. The object cannot span a page
+ * boundary. Returns 0 (and a locked page) if successful, -ENOTBLK if we
+ * cannot grab the page, or the usual negative errno.
+ */
+int
+xfile_get_page(
+ struct xfile *xf,
+ loff_t pos,
+ unsigned int len,
+ struct xfile_page *xfpage)
+{
+ struct inode *inode = file_inode(xf->file);
+ struct address_space *mapping = inode->i_mapping;
+ const struct address_space_operations *aops = mapping->a_ops;
+ struct page *page = NULL;
+ void *fsdata = NULL;
+ loff_t key = round_down(pos, PAGE_SIZE);
+ unsigned int pflags;
+ int error;
+
+ if (inode->i_sb->s_maxbytes - pos < len)
+ return -ENOMEM;
+ if (len > PAGE_SIZE - offset_in_page(pos))
+ return -ENOTBLK;
+
+ trace_xfile_get_page(xf, pos, len);
+
+ pflags = memalloc_nofs_save();
+
+ /*
+ * We call write_begin directly here to avoid all the freezer
+ * protection lock-taking that happens in the normal path. shmem
+ * doesn't support fs freeze, but lockdep doesn't know that and will
+ * trip over that.
+ */
+ error = aops->write_begin(NULL, mapping, key, PAGE_SIZE, &page,
+ &fsdata);
+ if (error)
+ goto out_pflags;
+
+ /* We got the page, so make sure we push out EOF. */
+ if (i_size_read(inode) < pos + len)
+ i_size_write(inode, pos + len);
+
+ /*
+ * If the page isn't up to date, fill it with zeroes before we hand it
+ * to the caller and make sure the backing store will hold on to them.
+ */
+ if (!PageUptodate(page)) {
+ void *kaddr;
+
+ kaddr = kmap_local_page(page);
+ memset(kaddr, 0, PAGE_SIZE);
+ kunmap_local(kaddr);
+ SetPageUptodate(page);
+ }
+
+ /*
+ * Mark each page dirty so that the contents are written to some
+ * backing store when we drop this buffer, and take an extra reference
+ * to prevent the xfile page from being swapped or removed from the
+ * page cache by reclaim if the caller unlocks the page.
+ */
+ set_page_dirty(page);
+ get_page(page);
+
+ xfpage->page = page;
+ xfpage->fsdata = fsdata;
+ xfpage->pos = key;
+out_pflags:
+ memalloc_nofs_restore(pflags);
+ return error;
+}
+
+/*
+ * Release the (locked) page for a memory object. Returns 0 or a negative
+ * errno.
+ */
+int
+xfile_put_page(
+ struct xfile *xf,
+ struct xfile_page *xfpage)
+{
+ struct inode *inode = file_inode(xf->file);
+ struct address_space *mapping = inode->i_mapping;
+ const struct address_space_operations *aops = mapping->a_ops;
+ unsigned int pflags;
+ int ret;
+
+ trace_xfile_put_page(xf, xfpage->pos, PAGE_SIZE);
+
+ /* Give back the reference that we took in xfile_get_page. */
+ put_page(xfpage->page);
+
+ pflags = memalloc_nofs_save();
+ ret = aops->write_end(NULL, mapping, xfpage->pos, PAGE_SIZE, PAGE_SIZE,
+ xfpage->page, xfpage->fsdata);
+ memalloc_nofs_restore(pflags);
+ memset(xfpage, 0, sizeof(struct xfile_page));
+
+ if (ret < 0)
+ return ret;
+ if (ret != PAGE_SIZE)
+ return -EIO;
+ return 0;
+}
diff --git a/fs/xfs/scrub/xfile.h b/fs/xfs/scrub/xfile.h
index 9328a37fedaa3..7065abd97a9a9 100644
--- a/fs/xfs/scrub/xfile.h
+++ b/fs/xfs/scrub/xfile.h
@@ -6,6 +6,12 @@
#ifndef __XFS_SCRUB_XFILE_H__
#define __XFS_SCRUB_XFILE_H__

+struct xfile_page {
+ struct page *page;
+ void *fsdata;
+ loff_t pos;
+};
+
struct xfile {
struct file *file;
};
@@ -54,4 +60,8 @@ struct xfile_stat {

int xfile_stat(struct xfile *xf, struct xfile_stat *statbuf);

+int xfile_get_page(struct xfile *xf, loff_t offset, unsigned int len,
+ struct xfile_page *xbuf);
+int xfile_put_page(struct xfile *xf, struct xfile_page *xbuf);
+
#endif /* __XFS_SCRUB_XFILE_H__ */