Received-SPF: pass (google.com: domain of linux-nfs-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
IronPort-SDR: GbtTGQ+LIQEViS39Onovks2tUDOKKPU08qCafY5K9+vdym21FqKofkTnIdrJANf0p7lkfhRJrl
 S2tkbyTKSPrw==
IronPort-SDR: Awdi9Evv+UAQx0jH4ny/s7+Nxcmli85F+a73BOsSCHQvCG+q13xwJ2JLwUM5pKItlqpgm8qi5b
 o2XGvRLHUUbw==
Date:   Sun, 11 Oct 2020 22:28:18 -0700
From:   Ira Weiny <ira.weiny@intel.com>
To:     Coly Li <colyli@suse.de>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Kent Overstreet <kent.overstreet@gmail.com>, x86@kernel.org,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Fenghua Yu <fenghua.yu@intel.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-nvdimm@lists.01.org,
        linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
        linux-kselftest@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        kvm@vger.kernel.org, netdev@vger.kernel.org, bpf@vger.kernel.org,
        kexec@lists.infradead.org, linux-bcache@vger.kernel.org,
        linux-mtd@lists.infradead.org, devel@driverdev.osuosl.org,
        linux-efi@vger.kernel.org, linux-mmc@vger.kernel.org,
        linux-scsi@vger.kernel.org, target-devel@vger.kernel.org,
        linux-nfs@vger.kernel.org, ceph-devel@vger.kernel.org,
        linux-ext4@vger.kernel.org, linux-aio@kvack.org,
        io-uring@vger.kernel.org, linux-erofs@lists.ozlabs.org,
        linux-um@lists.infradead.org, linux-ntfs-dev@lists.sourceforge.net,
        reiserfs-devel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net,
        linux-nilfs@vger.kernel.org, cluster-devel@redhat.com,
        ecryptfs@vger.kernel.org, linux-cifs@vger.kernel.org,
        linux-btrfs@vger.kernel.org, linux-afs@lists.infradead.org,
        linux-rdma@vger.kernel.org, amd-gfx@lists.freedesktop.org,
        dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org,
        drbd-dev@lists.linbit.com, linux-block@vger.kernel.org,
        xen-devel@lists.xenproject.org, linux-cachefs@redhat.com,
        samba-technical@lists.samba.org, intel-wired-lan@lists.osuosl.org
Subject: Re: [PATCH RFC PKS/PMEM 48/58] drivers/md: Utilize new kmap_thread()
Message-ID: <20201012052817.GZ2046448@iweiny-DESK2.sc.intel.com>
References: <20201009195033.3208459-1-ira.weiny@intel.com>
 <20201009195033.3208459-49-ira.weiny@intel.com>
 <c802fbf4-f67a-b205-536d-9c71b440f9c8@suse.de>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <c802fbf4-f67a-b205-536d-9c71b440f9c8@suse.de>
User-Agent: Mutt/1.11.1 (2018-12-01)
Precedence: bulk

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
>