| Message ID | 20201009195033.3208459-49-ira.weiny@intel.com (mailing list archive) |
|---|---|
| State | RFC |
| Headers | show |
| Series | PMEM: Introduce stray write protection for PMEM | expand |
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); >
On Sat, Oct 10, 2020 at 10:20:34AM +0800, Coly Li wrote: > 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 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 >
On 2020/10/12 13:28, Ira Weiny wrote: > On Sat, Oct 10, 2020 at 10:20:34AM +0800, Coly Li wrote: >> 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 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. I understand it now, the idea is fine to me. Acked-by: Coly Li <colyli@suse.de> Thanks. Coly Li
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);