From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fabio M. De Francesco Date: Sat, 01 Jul 2023 15:45:24 +0200 Subject: [Cluster-devel] [PATCH v3 5/6] gfs2: Replace kmap() by kmap_local_page() in gfs2_read_super In-Reply-To: <7ad72f9d1a97d673483c206d8ac9a88f2e32d3b9.1688073459.git.drv@mailo.com> References: <7ad72f9d1a97d673483c206d8ac9a88f2e32d3b9.1688073459.git.drv@mailo.com> Message-ID: <4817807.GXAFRqVoOG@suse> List-Id: To: cluster-devel.redhat.com MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On gioved? 29 giugno 2023 23:51:53 CEST Deepak R Varma wrote: > The use of kmap() is being deprecated in favor of kmap_local_page(). > > There are two main problems with kmap(): (1) It comes with an overhead as > the mapping space is restricted and protected by a global lock for > synchronization and (2) it also requires global TLB invalidation when the > kmap?s pool wraps and it might block when the mapping space is fully > utilized until a slot becomes available. > > With kmap_local_page() the mappings are per thread, CPU local, can take > page faults, and can be called from any context (including interrupts). > It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore, > the tasks can be preempted and, when they are scheduled to run again, the > kernel virtual addresses are restored and still valid. > > Therefore, replace kmap() with kmap_local_page() in gfs2_read_super(). > > Suggested-by: Fabio M. De Francesco > Signed-off-by: Deepak R Varma > --- > Changes in v3: > - Patch included in patch set > > Changes in v2: > - None > > fs/gfs2/ops_fstype.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/fs/gfs2/ops_fstype.c b/fs/gfs2/ops_fstype.c > index 8a27957dbfee..80fe61662412 100644 > --- a/fs/gfs2/ops_fstype.c > +++ b/fs/gfs2/ops_fstype.c > @@ -264,9 +264,9 @@ static int gfs2_read_super(struct gfs2_sbd *sdp, sector_t > sector, int silent) __free_page(page); > return -EIO; > } > - p = kmap(page); > + p = kmap_local_page(page); > Deepak, Could this page ever come from ZONE_HIGHMEM? Can you please check whether we really need to kmap*() it or not? Fabio > > gfs2_sb_in(sdp, p); > - kunmap(page); > + kunmap_local(p); > __free_page(page); > return gfs2_check_sb(sdp, silent); > } > -- > 2.34.1