Re: [PATCH v7 3/5] mm/hugetlb: add support for mempolicy MPOL_PREFERRED_MANY

[Feng Tang <feng.tang@intel.com>]

On Mon, Aug 09, 2021 at 03:19:32PM +0200, Michal Hocko wrote:
[snip]
> > > Do you think you can provide same helpers for other policies as well?
> > > Maybe we can get rid of some other ifdefery as well.
> > 
> > Sure. I can make separate patch(es) for that.
> > 
> > And you mean helper like mpol_is_bind/default/local/preferred? 
> > 
> > I just run 'git-grep MPOL', and for places using "mode == MPOL_XXX",
> > mostly they are in mempolicy.[ch], the only another place is in
> > shmem.c, do we need to create all the helpers for it and the
> > potential future users? 
> 
> I would just go with those instances which need to ifdef for NUMA.
> Thanks!

Yes, following is a patch to remove one CONFIG_NUMA check, though
an bolder idea to extend the patch by removing the CONFIG_TMPFS
check in the same line.

Thanks,
Feng

---------8<---------------------------------

From 1a5858721ac8ce99c27c13d310bba2983dc73d97 Mon Sep 17 00:00:00 2001
From: Feng Tang <feng.tang@intel.com>
Date: Tue, 10 Aug 2021 17:00:59 +0800
Subject: [PATCH] mm: shmem: avoid open coded check for mempolicy's mode

Add a mempolicy helper to do the check, which can also remove
a CONFIG_NUMA option check.

Suggested-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Feng Tang <feng.tang@intel.com>
---
 include/linux/mempolicy.h | 14 ++++++++++++++
 mm/shmem.c                |  8 ++++----
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 60d5e6c3340c..8fc518ad4f3c 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h
@@ -192,6 +192,10 @@ static inline bool mpol_is_preferred_many(struct mempolicy *pol)
 	return  (pol->mode == MPOL_PREFERRED_MANY);
 }
 
+static inline bool mpol_is_default(struct mempolicy *pol)
+{
+	return  (pol->mode == MPOL_DEFAULT);
+}
 
 #else
 
@@ -287,6 +291,10 @@ static inline int mpol_parse_str(char *str, struct mempolicy **mpol)
 }
 #endif
 
+static inline void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
+{
+}
+
 static inline int mpol_misplaced(struct page *page, struct vm_area_struct *vma,
 				 unsigned long address)
 {
@@ -309,5 +317,11 @@ static inline bool mpol_is_preferred_many(struct mempolicy *pol)
 	return  false;
 }
 
+static inline bool mpol_is_default(struct mempolicy *pol)
+{
+	return  false;
+}
+
+
 #endif /* CONFIG_NUMA */
 #endif
diff --git a/mm/shmem.c b/mm/shmem.c
index 96f05f6af8bb..26b195209ef7 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1437,12 +1437,12 @@ static int shmem_writepage(struct page *page, struct writeback_control *wbc)
 	return 0;
 }
 
-#if defined(CONFIG_NUMA) && defined(CONFIG_TMPFS)
+#ifdef CONFIG_TMPFS
 static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
 {
 	char buffer[64];
 
-	if (!mpol || mpol->mode == MPOL_DEFAULT)
+	if (!mpol || mpol_is_default(mpol))
 		return;		/* show nothing */
 
 	mpol_to_str(buffer, sizeof(buffer), mpol);
@@ -1461,7 +1461,7 @@ static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
 	}
 	return mpol;
 }
-#else /* !CONFIG_NUMA || !CONFIG_TMPFS */
+#else /* !CONFIG_TMPFS */
 static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
 {
 }
@@ -1469,7 +1469,7 @@ static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
 {
 	return NULL;
 }
-#endif /* CONFIG_NUMA && CONFIG_TMPFS */
+#endif /* CONFIG_TMPFS */
 #ifndef CONFIG_NUMA
 #define vm_policy vm_private_data
 #endif
-- 
2.14.1