From: Ira Weiny <[email protected]>
These kmap() calls are localized to a single thread. To avoid the over
head of global PKRS updates use the new kmap_thread() call.
Cc: Coly Li <[email protected]> (maintainer:BCACHE (BLOCK LAYER CACHE))
Cc: Kent Overstreet <[email protected]> (maintainer:BCACHE (BLOCK LAYER CACHE))
Signed-off-by: Ira Weiny <[email protected]>
---
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);
--
2.28.0.rc0.12.gb6a658bd00c9
On Sat, Oct 10, 2020 at 10:20:34AM +0800, Coly Li wrote:
> On 2020/10/10 03:50, [email protected] wrote:
> > From: Ira Weiny <[email protected]>
> >
> > 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 for the feedback.
I'm going to hold off making any changes until others weigh in. FWIW, I kind
of like option 2 as well. But there is already kmap_atomic() so it seemed like
kmap_XXXX() was more in line with the current API.
Thanks,
Ira
>
> Thanks.
>
>
> Coly Li
>