Re: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

[Chunming Zhou]

Hi Roger,

I think this patch isn't need at all. You can directly read 
total_swap_pages variable in TTM. See the comment:

/* protected with swap_lock. reading in vm_swap_full() doesn't need lock */
long total_swap_pages;

there are many places using it directly, you just couldn't change its 
value. Reading it doesn't need lock.


Regards,

David Zhou


On 2018年01月29日 16:29, Roger He wrote:
ttm module needs it to determine its internal parameter setting.

Signed-off-by: Roger He <hongbo...@amd.com>
---
  include/linux/swap.h |  6 ++++++
  mm/swapfile.c        | 15 +++++++++++++++
  2 files changed, 21 insertions(+)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index c2b8128..708d66f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -484,6 +484,7 @@ extern int try_to_free_swap(struct page *);
  struct backing_dev_info;
  extern int init_swap_address_space(unsigned int type, unsigned long nr_pages);
  extern void exit_swap_address_space(unsigned int type);
+extern long get_total_swap_pages(void);
  
  #else /* CONFIG_SWAP */
  
@@ -516,6 +517,11 @@ static inline void show_swap_cache_info(void)
  {
  }
  
+long get_total_swap_pages(void)
+{
+       return 0;
+}
+
  #define free_swap_and_cache(e) ({(is_migration_entry(e) || 
is_device_private_entry(e));})
  #define swapcache_prepare(e) ({(is_migration_entry(e) || 
is_device_private_entry(e));})
  
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 3074b02..a0062eb 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -98,6 +98,21 @@ static atomic_t proc_poll_event = ATOMIC_INIT(0);
  
  atomic_t nr_rotate_swap = ATOMIC_INIT(0);
  
+/*
+ * expose this value for others use
+ */
+long get_total_swap_pages(void)
+{
+       long ret;
+
+       spin_lock(&swap_lock);
+       ret = total_swap_pages;
+       spin_unlock(&swap_lock);
+
+       return ret;
+}
+EXPORT_SYMBOL_GPL(get_total_swap_pages);
+
  static inline unsigned char swap_count(unsigned char ent)
  {
        return ent & ~SWAP_HAS_CACHE;       /* may include SWAP_HAS_CONT flag */