[PATCH v2] sysinfo: include availram field in sysinfo struct

Pintu Kumar
2022-01-07T18:09:05Z

The sysinfo member does not have any "available ram" field and
the bufferram field is not much helpful either, to get a rough
estimate of available ram needed for allocation.

One needs to parse MemAvailable field separately from /proc/meminfo
to get this info instead of directly getting if from sysinfo itself.

Thus, this patch introduce a new field as availram in sysinfo
so that all the info total/free/available can be retrieved from
one place itself.

There are couple of places in kernel as well where this can be improved.
For example:
In fs/proc/meminfo.c:
meminfo_proc_show:
si_meminfo(&i);
available = si_mem_available();
Now with this change the second call be avoided.
Thus, we can directly do:
show_val_kb(m, "MemAvailable: ", i.availram);

Note, this also requires update in procfs for free and other commands.
Like in free command as well we frist call sysinfo then again parse
/proc/meminfo to get available field.
This can be avoided too with higher kernel version.

A sample output with single sysinfo call is shown below:
Total RAM: 248376 kB
Free RAM: 231540 kB
Avail RAM: 230448 kB

Signed-off-by: Pintu Kumar <quic_pintu@quicinc.com>
Signed-off-by: Pintu Agarwal <pintu.ping@gmail.com>
---
include/uapi/linux/sysinfo.h | 3 ++-
kernel/sys.c | 4 ++++
mm/page_alloc.c | 2 ++
3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/sysinfo.h b/include/uapi/linux/sysinfo.h
index 435d5c2..fe84c6a 100644
--- a/include/uapi/linux/sysinfo.h
+++ b/include/uapi/linux/sysinfo.h
@@ -19,7 +19,8 @@ struct sysinfo {
__kernel_ulong_t totalhigh; /* Total high memory size */
__kernel_ulong_t freehigh; /* Available high memory size */
__u32 mem_unit; /* Memory unit size in bytes */
- char _f[20-2*sizeof(__kernel_ulong_t)-sizeof(__u32)]; /* Padding: libc5 uses this.. */
+ __kernel_ulong_t availram; /* Memory available for allocation */
+ char _f[20-3*sizeof(__kernel_ulong_t)-sizeof(__u32)]; /* Padding: libc5 uses this.. */
};

#endif /* _LINUX_SYSINFO_H */
diff --git a/kernel/sys.c b/kernel/sys.c
index ecc4cf0..7059515 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2671,6 +2671,7 @@ static int do_sysinfo(struct sysinfo *info)
info->freeram <<= bitcount;
info->sharedram <<= bitcount;
info->bufferram <<= bitcount;
+ info->availram <<= bitcount;
info->totalswap <<= bitcount;
info->freeswap <<= bitcount;
info->totalhigh <<= bitcount;
@@ -2700,6 +2701,7 @@ struct compat_sysinfo {
u32 freeram;
u32 sharedram;
u32 bufferram;
+ u32 availram;
u32 totalswap;
u32 freeswap;
u16 procs;
@@ -2732,6 +2734,7 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
s.freeram >>= bitcount;
s.sharedram >>= bitcount;
s.bufferram >>= bitcount;
+ s.availram >>= bitcount;
s.totalswap >>= bitcount;
s.freeswap >>= bitcount;
s.totalhigh >>= bitcount;
@@ -2747,6 +2750,7 @@ COMPAT_SYSCALL_DEFINE1(sysinfo, struct compat_sysinfo __user *, info)
s_32.freeram = s.freeram;
s_32.sharedram = s.sharedram;
s_32.bufferram = s.bufferram;
+ s_32.availram = s.availram;
s_32.totalswap = s.totalswap;
s_32.freeswap = s.freeswap;
s_32.procs = s.procs;
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index b5d62e1..5013c75 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -5786,6 +5786,7 @@ void si_meminfo(struct sysinfo *val)
val->sharedram = global_node_page_state(NR_SHMEM);
val->freeram = global_zone_page_state(NR_FREE_PAGES);
val->bufferram = nr_blockdev_pages();
+ val->availram = si_mem_available();
val->totalhigh = totalhigh_pages();
val->freehigh = nr_free_highpages();
val->mem_unit = PAGE_SIZE;
@@ -5807,6 +5808,7 @@ void si_meminfo_node(struct sysinfo *val, int nid)
val->totalram = managed_pages;
val->sharedram = node_page_state(pgdat, NR_SHMEM);
val->freeram = sum_zone_node_page_state(nid, NR_FREE_PAGES);
+ val->availram = si_mem_available();
#ifdef CONFIG_HIGHMEM
for (zone_type = 0; zone_type < MAX_NR_ZONES; zone_type++) {
struct zone *zone = &pgdat->node_zones[zone_type];
--
2.7.4