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:
quoted
From: Ira Weiny <redacted>
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 <redacted>
---
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