Re: [patch 4/4] dm-writecache: use new API for flushing

[Mike Snitzer <snitzer-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>]

On Wed, May 30 2018 at 10:09P -0400,
Mikulas Patocka <mpatocka-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> wrote:
 
> And what about this?
> #define WC_MODE_PMEM(wc)                        ((wc)->pmem_mode)
> 
> The code that I had just allowed the compiler to optimize out 
> persistent-memory code if we have DM_WRITECACHE_ONLY_SSD defined - and you 
> deleted it.
> 
> Most architectures don't have persistent memory and the dm-writecache 
> driver could work in ssd-only mode on them. On these architectures, I 
> define
> #define WC_MODE_PMEM(wc)                        false
> - and the compiler will just automatically remove the tests for that 
> condition and the unused branch. It does also eliminate unused static 
> functions.

Here is the patch that I just folded into the rebased version of
dm-writecache now in the dm-4.18 branch.

(I rebased ontop of Jens' latest block tree for 4.18 that now includes
the mempool_init changes, etc.)

---
 drivers/md/dm-writecache.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index fcbfaf7c27ec..691b5ffb799f 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -34,13 +34,21 @@
 #define BITMAP_GRANULARITY	PAGE_SIZE
 #endif
 
+#if defined(CONFIG_ARCH_HAS_PMEM_API) && IS_ENABLED(CONFIG_DAX_DRIVER)
+#define DM_WRITECACHE_HAS_PMEM
+#endif
+
+#ifdef DM_WRITECACHE_HAS_PMEM
 #define pmem_assign(dest, src)					\
 do {								\
 	typeof(dest) uniq = (src);				\
 	memcpy_flushcache(&(dest), &uniq, sizeof(dest));	\
 } while (0)
+#else
+#define pmem_assign(dest, src)	((dest)) = (src))
+#endif
 
-#if defined(__HAVE_ARCH_MEMCPY_MCSAFE) && defined(CONFIG_ARCH_HAS_PMEM_API)
+#if defined(__HAVE_ARCH_MEMCPY_MCSAFE) && defined(DM_WRITECACHE_HAS_PMEM)
 #define DM_WRITECACHE_HANDLE_HARDWARE_ERRORS
 #endif
 
@@ -87,8 +95,13 @@ struct wc_entry {
 #endif
 };
 
+#ifdef DM_WRITECACHE_HAS_PMEM
 #define WC_MODE_PMEM(wc)			((wc)->pmem_mode)
 #define WC_MODE_FUA(wc)				((wc)->writeback_fua)
+#else
+#define WC_MODE_PMEM(wc)			false
+#define WC_MODE_FUA(wc)				false
+#endif
 #define WC_MODE_SORT_FREELIST(wc)		(!WC_MODE_PMEM(wc))
 
 struct dm_writecache {
@@ -1857,7 +1870,7 @@ static int writecache_ctr(struct dm_target *ti, unsigned argc, char **argv)
 	if (!strcasecmp(string, "s")) {
 		wc->pmem_mode = false;
 	} else if (!strcasecmp(string, "p")) {
-#if defined(CONFIG_ARCH_HAS_PMEM_API) && IS_ENABLED(CONFIG_DAX_DRIVER)
+#ifdef DM_WRITECACHE_HAS_PMEM
 		wc->pmem_mode = true;
 		wc->writeback_fua = true;
 #else
-- 
2.15.0