On Fri, 2020-10-09 at 14:34 -0700, Eric Biggers wrote:
On Fri, Oct 09, 2020 at 12:49:57PM -0700, ira.weiny@intel.com wrote:
From: Ira Weiny ira.weiny@intel.com
The kmap() calls in this FS are localized to a single thread. To avoid the over head of global PKRS updates use the new kmap_thread() call.
Cc: Jaegeuk Kim jaegeuk@kernel.org Cc: Chao Yu chao@kernel.org Signed-off-by: Ira Weiny ira.weiny@intel.com
fs/f2fs/f2fs.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h index d9e52a7f3702..ff72a45a577e 100644 --- a/fs/f2fs/f2fs.h +++ b/fs/f2fs/f2fs.h @@ -2410,12 +2410,12 @@ static inline struct page *f2fs_pagecache_get_page( static inline void f2fs_copy_page(struct page *src, struct page *dst) {
- char *src_kaddr = kmap(src);
- char *dst_kaddr = kmap(dst);
- char *src_kaddr = kmap_thread(src);
- char *dst_kaddr = kmap_thread(dst);
memcpy(dst_kaddr, src_kaddr, PAGE_SIZE);
- kunmap(dst);
- kunmap(src);
- kunmap_thread(dst);
- kunmap_thread(src);
}
Wouldn't it make more sense to switch cases like this to kmap_atomic()? The pages are only mapped to do a memcpy(), then they're immediately unmapped.
On a VIPT/VIVT architecture, this is horrendously wasteful. You're taking something that was mapped at colour c_src mapping it to a new address src_kaddr, which is likely a different colour and necessitates flushing the original c_src, then you copy it to dst_kaddr, which is also likely a different colour from c_dst, so dst_kaddr has to be flushed on kunmap and c_dst has to be invalidated on kmap. What we should have is an architectural primitive for doing this, something like kmemcopy_arch(dst, src). PIPT architectures can implement it as the above (possibly losing kmap if they don't need it) but VIPT/VIVT architectures can set up a correctly coloured mapping so they can simply copy from c_src to c_dst without any need to flush and the data arrives cache hot at c_dst.
James