zram: correct flag name of ZRAM_ACCESS

Patch series "zram memory tracking", v5.

zRam as swap is useful for small memory device.  However, swap means
those pages on zram are mostly cold pages due to VM's LRU algorithm.
Especially, once init data for application are touched for launching,
they tend to be not accessed any more and finally swapped out.  zRAM can
store such cold pages as compressed form but it's pointless to keep in
memory.  As well, it's pointless to store incompressible pages to zram
so better idea is app developers manages them directly like free or
mlock rather than remaining them on heap.

This patch provides a debugfs /sys/kernel/debug/zram/zram0/block_state
to represent each block's state so admin can investigate what memory is
cold|incompressible|same page with using pagemap once the pages are
swapped out.

The output is as follows:
      300    75.033841 .wh
      301    63.806904 s..
      302    63.806919 ..h

First column is zram's block index and 3rh one represents symbol (s:
same page w: written page to backing store h: huge page) of the block
state.  Second column represents usec time unit of the block was last
accessed.  So above example means the 300th block is accessed at
75.033851 second and it was huge so it was written to the backing store.

This patch (of 4):

ZRAM_ACCESS is used for locking a slot of zram so correct the name.  It
is also not a common flag to indicate status of the block so move the
declare position on top of the flag.  Lastly, let's move the function to
the top of source code to be able to use it easily without forward
declaration.

Link: http://lkml.kernel.org/r/20180416090946.63057-2-minchan@kernel.org
Signed-off-by: Minchan Kim <minchan@kernel.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/block/zram/zram_drv.c

@@ -52,6 +52,16 @@ static size_t huge_class_size;
 
 static void zram_free_page(struct zram *zram, size_t index);
 
+static void zram_slot_lock(struct zram *zram, u32 index)
+{
+	bit_spin_lock(ZRAM_LOCK, &zram->table[index].value);
+}
+
+static void zram_slot_unlock(struct zram *zram, u32 index)
+{
+	bit_spin_unlock(ZRAM_LOCK, &zram->table[index].value);
+}
+
 static inline bool init_done(struct zram *zram)
 {
 	return zram->disksize;
@@ -753,16 +763,6 @@ static DEVICE_ATTR_RO(io_stat);
 static DEVICE_ATTR_RO(mm_stat);
 static DEVICE_ATTR_RO(debug_stat);
 
-static void zram_slot_lock(struct zram *zram, u32 index)
-{
-	bit_spin_lock(ZRAM_ACCESS, &zram->table[index].value);
-}
-
-static void zram_slot_unlock(struct zram *zram, u32 index)
-{
-	bit_spin_unlock(ZRAM_ACCESS, &zram->table[index].value);
-}
-
 static void zram_meta_free(struct zram *zram, u64 disksize)
 {
 	size_t num_pages = disksize >> PAGE_SHIFT;

drivers/block/zram/zram_drv.h

@@ -43,9 +43,9 @@
 
 /* Flags for zram pages (table[page_no].value) */
 enum zram_pageflags {
-	/* Page consists the same element */
-	ZRAM_SAME = ZRAM_FLAG_SHIFT,
-	ZRAM_ACCESS,	/* page is now accessed */
+	/* zram slot is locked */
+	ZRAM_LOCK = ZRAM_FLAG_SHIFT,
+	ZRAM_SAME,	/* Page consists the same element */
 	ZRAM_WB,	/* page is stored on backing_device */
 
 	__NR_ZRAM_PAGEFLAGS,