Messages in this thread | | | Date | Mon, 13 Jun 2022 20:39:13 +0200 | From | David Sterba <> | Subject | Re: [PATCH] btrfs: Replace kmap() with kmap_local_page() in zstd.c |
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On Sat, Jun 11, 2022 at 03:52:03PM +0200, Fabio M. De Francesco wrote: > The use of kmap() is being deprecated in favor of kmap_local_page(). With > kmap_local_page(), the mapping is per thread, CPU local and not globally > visible. > > Therefore, use kmap_local_page() / kunmap_local() in zstd.c because in > this file the mappings are per thread and are not visible in other > contexts; meanwhile refactor zstd_compress_pages() to comply with nested > local mapping / unmapping ordering rules. > > Tested with xfstests on a QEMU + KVM 32 bits VM with 4GB of RAM and > HIGHMEM64G enabled. > > Cc: Filipe Manana <fdmanana@kernel.org> > Suggested-by: Ira Weiny <ira.weiny@intel.com> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> > --- > > @@ -477,15 +479,16 @@ int zstd_compress_pages(struct list_head *ws, struct address_space *mapping, > /* Check if we need more input */ > if (workspace->in_buf.pos == workspace->in_buf.size) { > tot_in += PAGE_SIZE; > - kunmap(in_page); > + kunmap_local(workspace->out_buf.dst); > + kunmap_local((void *)workspace->in_buf.src);
Why is the cast needed? I see that it leads to a warning but we pass a const buffer and that breaks the API contract as in kunmap it would be accessed as non-const and potentially changed without warning or compiler error. If kunmap_local does not touch the buffer and 'const void*' would work too, then it should be fixed.
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