Switch xfile_obj_load to use xfile_get_page and xfile_put_page to access
the shmem page cache. The former uses shmem_get_folio(..., SGP_READ),
which returns a NULL folio for a hole instead of allocating one to
optimize the case where the caller is reading from a whole and doesn't
want to a zeroed folio to the page cache.
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
---
fs/xfs/scrub/xfile.c | 51 +++++++++++---------------------------------
1 file changed, 12 insertions(+), 39 deletions(-)
diff --git a/fs/xfs/scrub/xfile.c b/fs/xfs/scrub/xfile.c
index 987b03df241b02..3f9e416376d2f7 100644
--- a/fs/xfs/scrub/xfile.c
+++ b/fs/xfs/scrub/xfile.c
@@ -34,13 +34,6 @@
* xfiles assume that the caller will handle all required concurrency
* management; standard vfs locks (freezer and inode) are not taken. Reads
* and writes are satisfied directly from the page cache.
- *
- * NOTE: The current shmemfs implementation has a quirk that in-kernel reads
- * of a hole cause a page to be mapped into the file. If you are going to
- * create a sparse xfile, please be careful about reading from uninitialized
- * parts of the file. These pages are !Uptodate and will eventually be
- * reclaimed if not written, but in the short term this boosts memory
- * consumption.
*/
/*
@@ -117,58 +110,38 @@ xfile_obj_load(
size_t count,
loff_t pos)
{
- struct inode *inode = file_inode(xf->file);
- struct address_space *mapping = inode->i_mapping;
- struct page *page = NULL;
- unsigned int pflags;
- int error = 0;
-
if (count > MAX_RW_COUNT)
return -ENOMEM;
- if (inode->i_sb->s_maxbytes - pos < count)
+ if (file_inode(xf->file)->i_sb->s_maxbytes - pos < count)
return -ENOMEM;
trace_xfile_obj_load(xf, pos, count);
- pflags = memalloc_nofs_save();
while (count > 0) {
+ struct page *page;
unsigned int len;
len = min_t(ssize_t, count, PAGE_SIZE - offset_in_page(pos));
-
- /*
- * In-kernel reads of a shmem file cause it to allocate a page
- * if the mapping shows a hole. Therefore, if we hit ENOMEM
- * we can continue by zeroing the caller's buffer.
- */
- page = shmem_read_mapping_page_gfp(mapping, pos >> PAGE_SHIFT,
- __GFP_NOWARN);
- if (IS_ERR(page)) {
- error = PTR_ERR(page);
- if (error != -ENOMEM) {
- error = -ENOMEM;
- break;
- }
-
+ page = xfile_get_page(xf, pos, len, 0);
+ if (IS_ERR(page))
+ return -ENOMEM;
+ if (!page) {
+ /*
+ * No data stored at this offset, just zero the output
+ * buffer.
+ */
memset(buf, 0, len);
goto advance;
}
-
- /*
- * xfile pages must never be mapped into userspace, so
- * we skip the dcache flush.
- */
memcpy(buf, page_address(page) + offset_in_page(pos), len);
- put_page(page);
-
+ xfile_put_page(xf, page);
advance:
count -= len;
pos += len;
buf += len;
}
- memalloc_nofs_restore(pflags);
- return error;
+ return 0;
}
/*
--
2.39.2
