From a4fc4a0c45f2617c3aa8b693739de264e0c09909 Mon Sep 17 00:00:00 2001 From: "Matthew Wilcox (Oracle)" Date: Tue, 7 Nov 2023 21:26:40 +0000 Subject: [PATCH] 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: Matthew Wilcox (Oracle) Reviewed-by: Andreas Gruenbacher Cc: Darrick J. Wong Cc: Theodore Ts'o Signed-off-by: Andrew Morton --- fs/ext4/inline.c | 3 +-- include/linux/highmem.h | 38 ++++++++++++++++++++++++++++++++++++++ 2 files changed, 39 insertions(+), 2 deletions(-) diff --git a/fs/ext4/inline.c b/fs/ext4/inline.c index 9a84a5f9fef4..d5bd1e3a5d36 100644 --- a/fs/ext4/inline.c +++ b/fs/ext4/inline.c @@ -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); diff --git a/include/linux/highmem.h b/include/linux/highmem.h index be20cff4ba73..5ebd5e4dfbf8 100644 --- a/include/linux/highmem.h +++ b/include/linux/highmem.h @@ -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.