shmem: make shmem default size a define value

The default size of the shmem filesystem is currently set to 50% of memory using a magic token. This change makes it a define value, so that it is clearly denoted as a global value, and to make it easier to track down and identify.

No behavior is changed, and no additional processing is created.

Signed-off-by Gary B. Genett <[email protected]>

---
 mm/shmem.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

mm/shmem.c +3 -0

index cd570cc79c76..bc758cfb4cb6 100644
@@ -95,6 +95,9 @@ static struct vfsmount *shm_mnt;
 /* Symlink up to this size is kmalloc'ed instead of using a swappable page */
 #define SHORT_SYMLINK_LEN 128
 
+/* Default size of shmem filesystem */
+#define SHMEM_SIZE_DEFAULT (totalram_pages() / 2)
+
 /*
  * shmem_fallocate communicates with shmem_fault or shmem_writepage via
  * inode->i_private (with i_mutex making sure that it has only one user at

mm/shmem.c +1 -2

-	return min(nr_pages - totalhigh_pages(), nr_pages / 2);
+	return min(nr_pages - totalhigh_pages(), SHMEM_SIZE_DEFAULT);
 }
 #endif
 
--

2.15.2

Quoted 8 lines

mm/shmem.c +1 -1

@@ -125,14 +128,14 @@ struct shmem_options {
 #ifdef CONFIG_TMPFS
 static unsigned long shmem_default_max_blocks(void)
 {
-	return totalram_pages() / 2;
+	return SHMEM_SIZE_DEFAULT;
 }
 

mm/shmem.c struct shmem_options { · line 136

Quoted 3 lines

mm/shmem.c +0 -0

 static unsigned long shmem_default_max_inodes(void)
 {
 	unsigned long nr_pages = totalram_pages();

This is now unused.

Quoted 4 lines

mm/shmem.c +1 -1

-	return min(nr_pages - totalhigh_pages(), nr_pages / 2);
+	return min(nr_pages - totalhigh_pages(), SHMEM_SIZE_DEFAULT);
 }
 #endif

Quoted 8 lines

Quoted 8 lines

mm/shmem.c +1 -1

@@ -125,14 +128,14 @@ struct shmem_options {
 #ifdef CONFIG_TMPFS
 static unsigned long shmem_default_max_blocks(void)
 {
-	return totalram_pages() / 2;
+	return SHMEM_SIZE_DEFAULT;
 }
 

Quoted 5 lines

mm/shmem.c struct shmem_options { · line 136

Quoted 3 lines

mm/shmem.c +0 -0

 static unsigned long shmem_default_max_inodes(void)
 {
 	unsigned long nr_pages = totalram_pages();

This is now unused.

Mind telling me what I missed, Qian?

I pulled from:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git

Latest commit is:

2019-10-08 15:36:04 -0700 e3280b54afed870d531571212f1fc375df39b7d2 Merge tag 'led-fixes-for-5.4-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/j.anaszewski/linux-leds

My patch is based on that, where the above code still exists, and nr_pages is still referenced below. Apparently, it is making totalram_pages atomic, according to the commit that changed it:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/diff/mm/shmem.c?id=ca79b0c211af63fa3276f0e3fd7dd9ada2439839

Should I be pulling from somewhere else, or also re-hacking nr_pages somehow?

-- Gary

Quoted 4 lines

Quoted 4 lines

mm/shmem.c +1 -1

-	return min(nr_pages - totalhigh_pages(), nr_pages / 2);
+	return min(nr_pages - totalhigh_pages(), SHMEM_SIZE_DEFAULT);
 }
 #endif

Quoted 1 line

Should I be pulling from somewhere else, or also re-hacking nr_pages somehow?

Ah, you are right that nr_pages is still referenced, but then there could a potentially out of sync? Would that be a problem? Is the compiler just smart enough to call totalram_pages() only once?

CPU0: CPU1:
unsigned long nr_pages = totalram_pages();
totalram_pages_inc()
min(nr_pages - totalhigh_pages(), SHMEM_SIZE_DEFAULT);