On 2020/10/10 03:50, ira.weiny@intel.com wrote:
From: Ira Weiny ira.weiny@intel.com
These kmap() calls are localized to a single thread. To avoid the over head of global PKRS updates use the new kmap_thread() call.
Hi Ira,
There were a number of options considered.
1) Attempt to change all the thread local kmap() calls to kmap_atomic() 2) Introduce a flags parameter to kmap() to indicate if the mapping should be global or not 3) Change ~20-30 call sites to 'kmap_global()' to indicate that they require a global mapping of the pages 4) Change ~209 call sites to 'kmap_thread()' to indicate that the mapping is to be used within that thread of execution only
I copied the above information from patch 00/58 to this message. The idea behind kmap_thread() is fine to me, but as you said the new api is very easy to be missed in new code (even for me). I would like to be supportive to option 2) introduce a flag to kmap(), then we won't forget the new thread-localized kmap method, and people won't ask why a _thread() function is called but no kthread created.
Thanks.
Coly Li
Cc: Coly Li colyli@suse.de (maintainer:BCACHE (BLOCK LAYER CACHE)) Cc: Kent Overstreet kent.overstreet@gmail.com (maintainer:BCACHE (BLOCK LAYER CACHE)) Signed-off-by: Ira Weiny ira.weiny@intel.com
drivers/md/bcache/request.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c index c7cadaafa947..a4571f6d09dd 100644 --- a/drivers/md/bcache/request.c +++ b/drivers/md/bcache/request.c @@ -44,10 +44,10 @@ static void bio_csum(struct bio *bio, struct bkey *k) uint64_t csum = 0; bio_for_each_segment(bv, bio, iter) {
void *d = kmap(bv.bv_page) + bv.bv_offset;
void *d = kmap_thread(bv.bv_page) + bv.bv_offset;csum = bch_crc64_update(csum, d, bv.bv_len);
kunmap(bv.bv_page);
kunmap_thread(bv.bv_page);k->ptr[KEY_PTRS(k)] = csum & (~0ULL >> 1);