Hi,

Here I am trying to introduce a new feature in kernel called "Agg= ressive Low Memory Booster".

The main advantage of this will be= to boost the available free memory of the system to "certain level" during= extremely low memory condition.

Please provide y= our comments to improve further.

Can it be used along with vmpressure_fd ???=

It can be invoked as follows:

a) Automatically by kernel memory managem= ent when the memory threshold falls below 10MB.

&= nbsp; b) From user space program/scr= ipts by passing the "required amount of memory to be reclaimed".

Example: echo 100 > /dev/shrink= mem

c) using sys interface - /sys/kernel/debug/shrinkallmem

= ; d) using an ioctl call and returni= ng number of pages reclaimed.

= e) using a new system call - shrinkallmem(&n= rpages);

f) During CMA to reclaim and shrink a specific CMA regions.

Here is the = snapshot of the write call:

+static ssize_t shrinkmem_write(struct file *fil= e, const char *buff,
+          &nb= sp;            =          size_t length, loff_t *pos= )
+{
+        int ret =3D -1;
+=         unsigned long memsize =3D 0;
= +        unsigned long nr_reclaim =3D 0;=
+        unsigned long pages =3D 0;<= br>+        ret =3D kstrtoul_from_user(b= uff, length, 0, &memsize);
+      &nbs= p; if (ret < 0) {
+        &n= bsp;       printk(KERN_ERR "[SHRINKMEM]: kstr= toul_from_user: Failed !\n");
+       = ;         return -1;
+        }
+   = ;     printk(KERN_INFO "[SHRINKMEM]: memsize(in MB) =3D= %ld\n",
+          &n= bsp;            = ;         (unsigned long)memsize);<= br>+        memsize =3D memsize*(1024UL*= 1024UL);
+        nr_reclaim =3D mems= ize / PAGE_SIZE;
+        pages =3D s= hrink_all_memory(nr_reclaim);
+       = ; printk(KERN_INFO "<SHRINKMEM>: Number of Pages Freed: %lu\n", pages= );
+        return pages;
+}

Please note: This requires CONFIG_HIBERNATION to be permanently enabled in the ke= rnel.

Several experiments have been performed on Ubuntu(kernel 3.3) = to verify it under low memory conditions.

Following are some results obt= ained:

-------------------------------------

Node 0, zone &nbs= p;    DMA    290    115 &= nbsp;    0      0   =    0      0     = ; 0      0      0 &n= bsp;    0      0
Node 0, zone&nb= sp; Normal    304    540  &nb= sp; 116     13      2 &nb= sp;    2      0   &n= bsp; 0      0      = 0      0
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
     &n= bsp;       total     = ; used       free     shar= ed    buffers     cached
Mem: &n= bsp;         497   &= nbsp;    487        = 10          0  &nbs= p;      63      &nbs= p; 303
-/+ buffers/cache:        120&= nbsp;       376
Swap:   &nb= sp;     1458       &= nbsp; 34       1424
Total:  &nbs= p;     1956        5= 22       1434
=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
Total Memory Freed: 342= MB
Total Memory Freed: 53 MB
Total Memory Freed: 23 MB
Total Memory Freed: 10 MB
Total Memory Freed: 15= MB
Total Memory Freed: -1 MB
Node 0, zone    &nb= sp; DMA      6      6&nbs= p;     7      8  &nb= sp; 10      9      = 7      4      1 &nbs= p;    0      0
Node 0, zone = ; Normal   2129   2612   2166 &nbs= p; 1723   1260    759    359 &= nbsp; 108     10      0&= nbsp;     0
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
      = ;       total     &n= bsp; used       free     shar= ed    buffers     cached
Mem: &n= bsp;         497   &= nbsp;     47        = 449          0  &nbs= p;       0      = ;    5
-/+ buffers/cache:     &n= bsp;   41        455
Swap:&= nbsp;        1458    = ;     97       1361
To= tal:        1956    =     145       1811
=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D

It was verified using a sample shell script "re= claim_memory.sh" which keeps recovering memory by doing "echo 500 > /dev= /shrinkmem" until no further reclaim is possible.

The experiments were p= erformed with various scenarios as follows:

a) Just after the boot up - (could recover around 150MB with 512MB RAM)

b) After running many applicati= ons include youtube videos, large tar files download -

[until free mem becomes < 10MB]

[Could recover around 300MB in one shot]

c) Run reclaim, while download is in progress and video still play= ing - (Not applications killed)

d) revoke all back= ground applications again, after running reclaim - (No impact, normal behav= ior)

[Just it took little extra time= to launch, as if it was launched for first time]

Please see more discussions on this in t= he last year mailing list:

https://lkml.org/lkml/2012/4/15/35
=

Thank You!

With regards,

Pintu Kumar

Samsung - India

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