Commit a4fc4a0c authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle) Committed by Andrew Morton
Browse files

mm: add folio_zero_tail() and use it in ext4 

Patch series "Add folio_zero_tail() and folio_fill_tail()".

I'm trying to make it easier for filesystems with tailpacking / stuffing /
inline data to use folios.  The primary function here is
folio_fill_tail().  You give it a pointer to memory where the data
currently is, and it takes care of copying it into the folio at that
offset.  That works for gfs2 & iomap.  Then There's Ext4.  Rather than gin
up some kind of specialist "Here's a two pointers to two blocks of memory"
routine, just let it do its current thing, and let it call
folio_zero_tail(), which is also called by folio_fill_tail().

Other filesystems can be converted later; these ones seemed like good
examples as they're already partly or completely converted to folios.


This patch (of 3):

Instead of unmapping the folio after copying the data to it, then mapping
it again to zero the tail, provide folio_zero_tail() to zero the tail of
an already-mapped folio.

[akpm@linux-foundation.org: fix kerneldoc argument ordering]
Link: https://lkml.kernel.org/r/20231107212643.3490372-1-willy@infradead.org
Link: https://lkml.kernel.org/r/20231107212643.3490372-2-willy@infradead.org


Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarAndreas Gruenbacher <agruenba@redhat.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
parent 600bca58

fs/ext4/inline.c

+1 −2
Original line number Diff line number Diff line
@@ -502,9 +502,8 @@ static int ext4_read_inline_folio(struct inode *inode, struct folio *folio) 
	BUG_ON(len > PAGE_SIZE);

	kaddr = kmap_local_folio(folio, 0);

	ret = ext4_read_inline_data(inode, kaddr, len, &iloc);

	flush_dcache_folio(folio);

	kaddr = folio_zero_tail(folio, len, kaddr + len);

	kunmap_local(kaddr);

	folio_zero_segment(folio, len, folio_size(folio));

	folio_mark_uptodate(folio);

	brelse(iloc.bh);

include/linux/highmem.h

+38 −0
Original line number Diff line number Diff line
@@ -483,6 +483,44 @@ static inline void memcpy_to_folio(struct folio *folio, size_t offset, 
	flush_dcache_folio(folio);

}



/**

 * folio_zero_tail - Zero the tail of a folio.

 * @folio: The folio to zero.

 * @offset: The byte offset in the folio to start zeroing at.

 * @kaddr: The address the folio is currently mapped to.

 *

 * If you have already used kmap_local_folio() to map a folio, written

 * some data to it and now need to zero the end of the folio (and flush

 * the dcache), you can use this function.  If you do not have the

 * folio kmapped (eg the folio has been partially populated by DMA),

 * use folio_zero_range() or folio_zero_segment() instead.

 *

 * Return: An address which can be passed to kunmap_local().

 */

static inline __must_check void *folio_zero_tail(struct folio *folio,

		size_t offset, void *kaddr)

{

	size_t len = folio_size(folio) - offset;



	if (folio_test_highmem(folio)) {

		size_t max = PAGE_SIZE - offset_in_page(offset);



		while (len > max) {

			memset(kaddr, 0, max);

			kunmap_local(kaddr);

			len -= max;

			offset += max;

			max = PAGE_SIZE;

			kaddr = kmap_local_folio(folio, offset);

		}

	}



	memset(kaddr, 0, len);

	flush_dcache_folio(folio);



	return kaddr;

}



/**

 * memcpy_from_file_folio - Copy some bytes from a file folio.

 * @to: The destination buffer.