Subject: Re: [PATCH] mm: cma: Discard clean pages during contiguous allocation instead of migration

From: Andrew Morton <[email-masked]>
Date: Thu, 13 Sep 2012 15:19:22 -0700

On Thu, 13 Sep 2012 21:17:19 +0200
Geert Uytterhoeven <[email-masked]> wrote:

> On Tue, Sep 11, 2012 at 2:41 AM, Minchan Kim <[email-masked]> wrote:
> > --- a/mm/vmscan.c
> > +++ b/mm/vmscan.c
> > @@ -674,8 +674,10 @@ static enum page_references page_check_references(struct page *page,
> >  static unsigned long shrink_page_list(struct list_head *page_list,
> >                                       struct zone *zone,
> >                                       struct scan_control *sc,
> > +                                     enum ttu_flags ttu_flags,
> 
> "enum ttu_flags" is defined on CONFIG_MMU=y only, causing on nommu:
> 
> mm/vmscan.c:677:26: error: parameter 4 ('ttu_flags') has incomplete type
> mm/vmscan.c:987:5: error: 'TTU_UNMAP' undeclared (first use in this function)
> mm/vmscan.c:987:15: error: 'TTU_IGNORE_ACCESS' undeclared (first use
> in this function)
> mm/vmscan.c:1312:56: error: 'TTU_UNMAP' undeclared (first use in this function)
> 
> E.g.
> http://kisskb.ellerman.id.au/kisskb/buildresult/7191694/ (h8300-defconfig)
> http://kisskb.ellerman.id.au/kisskb/buildresult/7191858/ (sh-allnoconfig)

hm, OK, the means by which current mainline avoids build errors is
either clever or lucky.

			switch (try_to_unmap(page, TTU_UNMAP)) {

gets preprocessed into

			switch (2) {

so the cmopiler never gets to see the TTU_ symbol at all.  Because it
happens to be inside the try_to_unmap() call.

I guess we can just make ttu_flags visible to NOMMU:

--- a/include/linux/rmap.h~mm-cma-discard-clean-pages-during-contiguous-allocation-instead-of-migration-fix-fix
+++ a/include/linux/rmap.h
@@ -71,6 +71,17 @@ struct anon_vma_chain {
 #endif
 };
 
+enum ttu_flags {
+	TTU_UNMAP = 0,			/* unmap mode */
+	TTU_MIGRATION = 1,		/* migration mode */
+	TTU_MUNLOCK = 2,		/* munlock mode */
+	TTU_ACTION_MASK = 0xff,
+
+	TTU_IGNORE_MLOCK = (1 << 8),	/* ignore mlock */
+	TTU_IGNORE_ACCESS = (1 << 9),	/* don't age */
+	TTU_IGNORE_HWPOISON = (1 << 10),/* corrupted page is recoverable */
+};
+
 #ifdef CONFIG_MMU
 static inline void get_anon_vma(struct anon_vma *anon_vma)
 {
@@ -164,16 +175,6 @@ int page_referenced(struct page *, int i
 int page_referenced_one(struct page *, struct vm_area_struct *,
 	unsigned long address, unsigned int *mapcount, unsigned long *vm_flags);
 
-enum ttu_flags {
-	TTU_UNMAP = 0,			/* unmap mode */
-	TTU_MIGRATION = 1,		/* migration mode */
-	TTU_MUNLOCK = 2,		/* munlock mode */
-	TTU_ACTION_MASK = 0xff,
-
-	TTU_IGNORE_MLOCK = (1 << 8),	/* ignore mlock */
-	TTU_IGNORE_ACCESS = (1 << 9),	/* don't age */
-	TTU_IGNORE_HWPOISON = (1 << 10),/* corrupted page is recoverable */
-};
 #define TTU_ACTION(x) ((x) & TTU_ACTION_MASK)
 
 int try_to_unmap(struct page *, enum ttu_flags flags);
_