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Date: Sun, 11 Oct 2020 22:28:18 -0700 From: Ira Weiny <ira.weiny@...el.com> To: Coly Li <colyli@...e.de> Cc: Andrew Morton <akpm@...ux-foundation.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Andy Lutomirski <luto@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Kent Overstreet <kent.overstreet@...il.com>, x86@...nel.org, Dave Hansen <dave.hansen@...ux.intel.com>, Dan Williams <dan.j.williams@...el.com>, Fenghua Yu <fenghua.yu@...el.com>, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, linux-kselftest@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, kvm@...r.kernel.org, netdev@...r.kernel.org, bpf@...r.kernel.org, kexec@...ts.infradead.org, linux-bcache@...r.kernel.org, linux-mtd@...ts.infradead.org, devel@...verdev.osuosl.org, linux-efi@...r.kernel.org, linux-mmc@...r.kernel.org, linux-scsi@...r.kernel.org, target-devel@...r.kernel.org, linux-nfs@...r.kernel.org, ceph-devel@...r.kernel.org, linux-ext4@...r.kernel.org, linux-aio@...ck.org, io-uring@...r.kernel.org, linux-erofs@...ts.ozlabs.org, linux-um@...ts.infradead.org, linux-ntfs-dev@...ts.sourceforge.net, reiserfs-devel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net, linux-nilfs@...r.kernel.org, cluster-devel@...hat.com, ecryptfs@...r.kernel.org, linux-cifs@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-afs@...ts.infradead.org, linux-rdma@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, intel-gfx@...ts.freedesktop.org, drbd-dev@...ts.linbit.com, linux-block@...r.kernel.org, xen-devel@...ts.xenproject.org, linux-cachefs@...hat.com, samba-technical@...ts.samba.org, intel-wired-lan@...ts.osuosl.org Subject: Re: [PATCH RFC PKS/PMEM 48/58] drivers/md: Utilize new kmap_thread() On Sat, Oct 10, 2020 at 10:20:34AM +0800, Coly Li wrote: > On 2020/10/10 03:50, ira.weiny@...el.com wrote: > > From: Ira Weiny <ira.weiny@...el.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 >
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