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mm: add folio_zero_tail() and use it in ext4

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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: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: 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>
This commit is contained in:
Matthew Wilcox (Oracle) 2023-11-07 21:26:40 +00:00 committed by Andrew Morton
parent 600bca5805
commit a4fc4a0c45
2 changed files with 39 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
fs/ext4/inline.c
View File

@ -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);

38
include/linux/highmem.h
View File

@ -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.