[RFC PATCH V1] zram:calculate available memory when zram is used

[yong w <yongw.pur@gmail.com>]

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When zram is used, available+Swap free memory is obviously bigger than
I actually can use, because zram can compress memory by compression
algorithm and zram compressed data will occupy memory too.

So, I count the compression rate of zram in the kernel. The available
memory  is calculated as follows:
available + swapfree - swapfree * compress ratio
MemAvailable in /proc/meminfo returns available + zram will save space

Signed-off-by: wangyong <yongw.pur@gmail.com>
---
 drivers/block/zram/zcomp.h    |  1 +
 drivers/block/zram/zram_drv.c |  4 ++
 drivers/block/zram/zram_drv.h |  1 +
 fs/proc/meminfo.c             |  2 +-
 include/linux/swap.h          | 10 +++++
 mm/swapfile.c                 | 95
+++++++++++++++++++++++++++++++++++++++++++
 mm/vmscan.c                   |  1 +
 7 files changed, 113 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zcomp.h b/drivers/block/zram/zcomp.h
index 40f6420..deb2dbf 100644
--- a/drivers/block/zram/zcomp.h
+++ b/drivers/block/zram/zcomp.h
@@ -40,4 +40,5 @@ int zcomp_decompress(struct zcomp_strm *zstrm,
  const void *src, unsigned int src_len, void *dst);

 bool zcomp_set_max_streams(struct zcomp *comp, int num_strm);
+int get_zram_major(void);
 #endif /* _ZCOMP_H_ */
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index cf8deec..1c6cbd4 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -59,6 +59,10 @@ static void zram_free_page(struct zram *zram, size_t
index);
 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
  u32 index, int offset, struct bio *bio);

+int get_zram_major(void)
+{
+ return zram_major;
+}

 static int zram_slot_trylock(struct zram *zram, u32 index)
 {
diff --git a/drivers/block/zram/zram_drv.h b/drivers/block/zram/zram_drv.h
index 6e73dc3..5d8701a 100644
--- a/drivers/block/zram/zram_drv.h
+++ b/drivers/block/zram/zram_drv.h
@@ -88,6 +88,7 @@ struct zram_stats {
  atomic64_t bd_reads; /* no. of reads from backing device */
  atomic64_t bd_writes; /* no. of writes from backing device */
 #endif
+ atomic_t min_compr_ratio;
 };

 struct zram {
diff --git a/fs/proc/meminfo.c b/fs/proc/meminfo.c
index 6fa761c..f7bf350 100644
--- a/fs/proc/meminfo.c
+++ b/fs/proc/meminfo.c
@@ -57,7 +57,7 @@ static int meminfo_proc_show(struct seq_file *m, void *v)

  show_val_kb(m, "MemTotal:       ", i.totalram);
  show_val_kb(m, "MemFree:        ", i.freeram);
- show_val_kb(m, "MemAvailable:   ", available);
+ show_val_kb(m, "MemAvailable:   ", available + count_avail_swaps());
  show_val_kb(m, "Buffers:        ", i.bufferram);
  show_val_kb(m, "Cached:         ", cached);
  show_val_kb(m, "SwapCached:     ", total_swapcache_pages());
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 032485e..3225a2f 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -514,6 +514,8 @@ extern int init_swap_address_space(unsigned int type,
unsigned long nr_pages);
 extern void exit_swap_address_space(unsigned int type);
 extern struct swap_info_struct *get_swap_device(swp_entry_t entry);
 sector_t swap_page_sector(struct page *page);
+extern void update_zram_zstats(void);
+extern u64 count_avail_swaps(void);

 static inline void put_swap_device(struct swap_info_struct *si)
 {
@@ -684,6 +686,14 @@ static inline swp_entry_t get_swap_page(struct page
*page)
  return entry;
 }

+void update_zram_zstats(void)
+{
+}
+
+u64 count_avail_swaps(void)
+{
+}
+
 #endif /* CONFIG_SWAP */

 #ifdef CONFIG_THP_SWAP
diff --git a/mm/swapfile.c b/mm/swapfile.c
index cbb4c07..93a9dcb 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -44,6 +44,7 @@
 #include <asm/tlbflush.h>
 #include <linux/swapops.h>
 #include <linux/swap_cgroup.h>
+#include "../drivers/block/zram/zram_drv.h"

 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
  unsigned char);
@@ -3408,6 +3409,100 @@ SYSCALL_DEFINE2(swapon, const char __user *,
specialfile, int, swap_flags)
  return error;
 }

+u64 count_avail_swap(struct swap_info_struct *si)
+{
+ u64 result;
+ struct zram *z;
+ unsigned int free;
+ unsigned int ratio;
+
+ result = 0;
+ if (!si)
+ return 0;
+
+ //zram calculate available mem
+ if (si->flags & SWP_USED && si->swap_map) {
+ if (si->bdev->bd_disk->major == get_zram_major()) {
+ z = (struct zram *)si->bdev->bd_disk->private_data;
+ down_read(&z->init_lock);
+ ratio = atomic_read(&z->stats.min_compr_ratio);
+ free = (si->pages << (PAGE_SHIFT - 10))
+ - (si->inuse_pages << (PAGE_SHIFT - 10));
+ if (!ratio)
+ result += free / 2;
+ else
+ result = free * (100 - 10000 / ratio) / 100;
+ up_read(&z->init_lock);
+ }
+ } else
+ result += (si->pages << (PAGE_SHIFT - 10))
+ - (si->inuse_pages << (PAGE_SHIFT - 10));
+
+ return result;
+}
+
+u64 count_avail_swaps(void)
+{
+ int type;
+ u64 result;
+ struct swap_info_struct *si;
+
+ result = 0;
+ spin_lock(&swap_lock);
+ for (type = 0; type < nr_swapfiles; type++) {
+ si = swap_info[type];
+ spin_lock(&si->lock);
+ result += count_avail_swap(si);
+ spin_unlock(&si->lock);
+ }
+ spin_unlock(&swap_lock);
+
+ return result;
+}
+
+void update_zram_zstat(struct swap_info_struct *si)
+{
+ struct zram *z;
+ struct zram_stats *stat;
+ int ratio;
+ u64 orig_size, compr_data_size;
+
+ if (!si)
+ return;
+
+ //update zram min compress ratio
+ if (si->flags & SWP_USED && si->swap_map) {
+ if (si->bdev->bd_disk->major == get_zram_major()) {
+ z = (struct zram *)si->bdev->bd_disk->private_data;
+ down_read(&z->init_lock);
+ stat = &z->stats;
+ ratio = atomic_read(&stat->min_compr_ratio);
+ orig_size = atomic64_read(&stat->pages_stored) << PAGE_SHIFT;
+ compr_data_size = atomic64_read(&stat->compr_data_size);
+ if (compr_data_size && (!ratio
+     || ((orig_size * 100) / compr_data_size < ratio)))
+ atomic_set(&stat->min_compr_ratio,
+    (orig_size * 100) / compr_data_size);
+ up_read(&z->init_lock);
+ }
+ }
+}
+
+void update_zram_zstats(void)
+{
+ int type;
+ struct swap_info_struct *si;
+
+ spin_lock(&swap_lock);
+ for (type = 0; type < nr_swapfiles; type++) {
+ si = swap_info[type];
+ spin_lock(&si->lock);
+ update_zram_zstat(si);
+ spin_unlock(&si->lock);
+ }
+ spin_unlock(&swap_lock);
+}
+
 void si_swapinfo(struct sysinfo *val)
 {
  unsigned int type;
diff --git a/mm/vmscan.c b/mm/vmscan.c
index eb31452..ffaf59b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4159,6 +4159,7 @@ static int kswapd(void *p)
  alloc_order);
  reclaim_order = balance_pgdat(pgdat, alloc_order,
  highest_zoneidx);
+ update_zram_zstats();
  if (reclaim_order < alloc_order)
  goto kswapd_try_sleep;
  }
-- 
2.7.4

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