fs: convert core functions to zero_user_page

It's very common for file systems to need to zero part or all of a page,
the simplist way is just to use kmap_atomic() and memset().  There's
actually a library function in include/linux/highmem.h that does exactly
that, but it's confusingly named memclear_highpage_flush(), which is
descriptive of *how* it does the work rather than what the *purpose* is.
So this patchset renames the function to zero_user_page(), and calls it
from the various places that currently open code it.

This first patch introduces the new function call, and converts all the
core kernel callsites, both the open-coded ones and the old
memclear_highpage_flush() ones.  Following this patch is a series of
conversions for each file system individually, per AKPM, and finally a
patch deprecating the old call.  The diffstat below shows the entire
patchset.

[akpm@linux-foundation.org: fix a few things]
Signed-off-by: Nate Diller <nate.diller@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 1 insertions, 6 deletions

diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index cbb335813ec0..1b49dab9b25d 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -434,7 +434,6 @@ xip_truncate_page(struct address_space *mapping, loff_t from)
         unsigned blocksize;
         unsigned length;
         struct page *page;
-        void *kaddr;
 
         BUG_ON(!mapping->a_ops->get_xip_page);
 
@@ -458,11 +457,7 @@ xip_truncate_page(struct address_space *mapping, loff_t from)
                 else
                         return PTR_ERR(page);
         }
-        kaddr = kmap_atomic(page, KM_USER0);
-        memset(kaddr + offset, 0, length);
-        kunmap_atomic(kaddr, KM_USER0);
-
-        flush_dcache_page(page);
+        zero_user_page(page, offset, length, KM_USER0);
         return 0;
 }
 EXPORT_SYMBOL_GPL(xip_truncate_page);