+ mm-add-folio_zero_tail-and-use-it-in-ext4.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: add folio_zero_tail() and use it in ext4
has been added to the -mm mm-unstable branch.  Its filename is
     mm-add-folio_zero_tail-and-use-it-in-ext4.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-add-folio_zero_tail-and-use-it-in-ext4.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Subject: mm: add folio_zero_tail() and use it in ext4
Date: Tue, 7 Nov 2023 21:26:40 +0000

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.

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: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Darrick J. Wong <djwong@kernel.org>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 fs/ext4/inline.c        |    3 +--
 include/linux/highmem.h |   38 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+), 2 deletions(-)

--- a/fs/ext4/inline.c~mm-add-folio_zero_tail-and-use-it-in-ext4
+++ a/fs/ext4/inline.c
@@ -502,9 +502,8 @@ static int ext4_read_inline_folio(struct
 	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);
 
--- a/include/linux/highmem.h~mm-add-folio_zero_tail-and-use-it-in-ext4
+++ a/include/linux/highmem.h
@@ -484,6 +484,44 @@ static inline void memcpy_to_folio(struc
 }
 
 /**
+ * folio_zero_tail - Zero the tail of a folio.
+ * @folio: The folio to zero.
+ * @kaddr: The address the folio is currently mapped to.
+ * @offset: The byte offset in the folio to start zeroing at.
+ *
+ * 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.
  * @folio: The folio to copy from.
_

Patches currently in -mm which might be from willy@infradead.org are

mm-add-folio_zero_tail-and-use-it-in-ext4.patch
mm-add-folio_fill_tail-and-use-it-in-iomap.patch
gfs2-convert-stuffed_readpage-to-stuffed_read_folio.patch
mm-remove-test_set_page_writeback.patch
afs-do-not-test-the-return-value-of-folio_start_writeback.patch
smb-do-not-test-the-return-value-of-folio_start_writeback.patch
mm-return-void-from-folio_start_writeback-and-related-functions.patch
mm-make-mapping_evict_folio-the-preferred-way-to-evict-clean-folios.patch
mm-convert-__do_fault-to-use-a-folio.patch
mm-use-mapping_evict_folio-in-truncate_error_page.patch
mm-convert-soft_offline_in_use_page-to-use-a-folio.patch
mm-convert-isolate_page-to-mf_isolate_folio.patch
mm-remove-invalidate_inode_page.patch