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

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Discussed with Roger just now, we can try "void si_swapinfo(struct sysinfo *val)" function to get the total swap space.

Regards,

David Zhou


On 2018年01月31日 16:12, Christian König wrote:
Yeah, indeed. But what we could do is to rely on a fixed limit like the Intel driver does and I suggested before.

E.g. don't copy anything into a shmemfile when there is only x MB of swap space left.

Roger can you test that approach once more with your fix for the OOM issues in the page fault handler?

Thanks,
Christian.

Am 31.01.2018 um 09:08 schrieb He, Roger:
    I think this patch isn't need at all. You can directly read total_swap_pages variable in TTM.

Because the variable is not exported by EXPORT_SYMBOL_GPL. So direct using will result in:
"WARNING: "total_swap_pages" [drivers/gpu/drm/ttm/ttm.ko] undefined!".

Thanks
Roger(Hongbo.He)
-----Original Message-----
From: dri-devel [mailto:dri-devel-bounces@xxxxxxxxxxxxxxxxxxxxx] On Behalf Of Chunming Zhou
Sent: Wednesday, January 31, 2018 3:15 PM
To: He, Roger <Hongbo.He@xxxxxxx>; dri-devel@xxxxxxxxxxxxxxxxxxxxx
Cc: linux-mm@xxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Koenig, Christian <Christian.Koenig@xxxxxxx> Subject: Re: [PATCH] mm/swap: add function get_total_swap_pages to expose total_swap_pages

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.He@xxxxxxx>
---
   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 */
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