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Date: Thu, 9 Nov 2023 22:50:08 +0100 From: Andreas Gruenbacher <agruenba@...hat.com> To: "Matthew Wilcox (Oracle)" <willy@...radead.org> Cc: Andrew Morton <akpm@...ux-foundation.org>, linux-ext4@...r.kernel.org, gfs2@...ts.linux.dev, linux-fsdevel@...r.kernel.org, linux-xfs@...r.kernel.org, "Darrick J . Wong" <djwong@...nel.org>, linux-erofs@...ts.ozlabs.org, "Theodore Ts'o" <tytso@....edu>, Andreas Dilger <adilger.kernel@...ger.ca> Subject: Re: [PATCH 1/3] mm: Add folio_zero_tail() and use it in ext4 Hi Willy, On Tue, Nov 7, 2023 at 10:27 PM Matthew Wilcox (Oracle) <willy@...radead.org> wrote: > 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. > > Signed-off-by: Matthew Wilcox (Oracle) <willy@...radead.org> > --- > 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 4cacc0e43b51..1b81416196dd 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. > + * @kaddr: The address the folio is currently mapped to. > + * @offset: The byte offset in the folio to start zeroing at. > + * As Andrew has pointed out, the order of the arguments in the description doesn't match the order in the function definition. Other than that, this patch looks good, so Reviewed-by: Andreas Gruenbacher <agruenba@...hat.com> > + * 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. > -- > 2.42.0 > Thanks, Andreas
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