| Message ID | 20221012112323.23283-1-fmdefrancesco@gmail.com (mailing list archive) |
|---|---|
| State | Not Applicable |
| Headers | show |
| Series | fs/fuse: Replace kmap() with kmap_local_page() | expand |
| Context | Check | Description |
|---|---|---|
| netdev/tree_selection | success | Not a local patch |
On Wed, 12 Oct 2022 at 13:38, Fabio M. De Francesco <fmdefrancesco@gmail.com> 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 fuse_readdir_cached(), > it being the only call site of kmap() currently left in fs/fuse. > > Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@intel.com> > Suggested-by: Ira Weiny <ira.weiny@intel.com> > Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> Applied, thanks. Miklos
diff --git a/fs/fuse/readdir.c b/fs/fuse/readdir.c index b4e565711045..9e40c19e90dc 100644 --- a/fs/fuse/readdir.c +++ b/fs/fuse/readdir.c @@ -539,9 +539,9 @@ static int fuse_readdir_cached(struct file *file, struct dir_context *ctx) * Contents of the page are now protected against changing by holding * the page lock. */ - addr = kmap(page); + addr = kmap_local_page(page); res = fuse_parse_cache(ff, addr, size, ctx); - kunmap(page); + kunmap_local(addr); unlock_page(page); put_page(page);
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 fuse_readdir_cached(), it being the only call site of kmap() currently left in fs/fuse. Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@intel.com> Suggested-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Fabio M. De Francesco <fmdefrancesco@gmail.com> --- These changes are not tested in a 32 bits VM as I use to do with other more problematic conversions. Mere code inspection makes me reasonably think that the rules of local mappings are not violated by this conversion. Furthermore, I have no idea how to test this code. If maintainers think that tests are absolutely necessary, any hints about how to perform them would be greatly appreciated. fs/fuse/readdir.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)