Introducing Aggressive Low Memory Booster [1]

[PINTU KUMAR]

Hi,

Can anybody provide any inputs/suggestions/improvements on the following.

According to my experiments these proved to be a useful utility during low memory condition on the embedded devices.
Is there something wrong I am doing?

Please provide your suggestions.

Thanks,
Pintu



>________________________________
> From: PINTU KUMAR <pintu_agarwal at yahoo.com>
>To: "linux-mm at kvack.org" <linux-mm at kvack.org>; "linux-kernel at vger.kernel.org" <linux-kernel at vger.kernel.org> 
>Cc: "linux-arm-kernel at lists.infradead.org" <linux-arm-kernel at lists.infradead.org>; "pintu.k at samsung.com" <pintu.k at samsung.com>; Anton Vorontsov <anton.vorontsov at linaro.org>; Alan Cox <alan at lxorguk.ukuu.org.uk>; richard -rw- weinberger <richard.weinberger at gmail.com>; "patches at linaro.org" <patches at linaro.org>; Mel Gorman <mgorman at suse.de>; Wanpeng Li <liwanp at linux.vnet.ibm.com> 
>Sent: Sunday, 13 January 2013 9:02 PM
>Subject: Introducing Aggressive Low Memory Booster [1]
> 
>
>Hi,
>
>
>Here I am trying to introduce a new feature in kernel called "Aggressive 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 your comments to improve further.
>Can it be used along with vmpressure_fd ???
>
>
>
>It can be invoked as follows:
>    a) Automatically by kernel memory management when the memory threshold falls below 10MB.
>    b) From user space program/scripts by passing the "required amount of memory to be reclaimed".
>    Example: echo 100 > /dev/shrinkmem
>    c) using sys interface - /sys/kernel/debug/shrinkallmem
>    d) using an ioctl call and returning number of pages reclaimed.
>    e) using a new system call - shrinkallmem(&nrpages);
>    f) During CMA to reclaim and shrink a specific CMA regions.
>
>
>
>I have developed a kernel module to verify the (b) part.
>
>
>Here is the snapshot of the write call:
>+static ssize_t shrinkmem_write(struct file *file, const char *buff,
>+                                size_t length, loff_t *pos)
>+{
>+        int ret = -1;
>+        unsigned long memsize = 0;
>+        unsigned long nr_reclaim = 0;
>+        unsigned long pages = 0;
>+        ret = kstrtoul_from_user(buff, length, 0, &memsize);
>+        if (ret < 0) {
>+                printk(KERN_ERR "[SHRINKMEM]: kstrtoul_from_user: Failed !\n");
>+                return
-1;
>+        }
>+        printk(KERN_INFO "[SHRINKMEM]: memsize(in MB) = %ld\n",
>+                                (unsigned long)memsize);
>+        memsize = memsize*(1024UL*1024UL);
>+        nr_reclaim = memsize / PAGE_SIZE;
>+        pages = shrink_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 kernel.
>
>
>Several experiments have been performed on Ubuntu(kernel 3.3) to verify it under low memory conditions.
>
>
>Following are some results obtained:
>-------------------------------------
>
>Node 0, zone      DMA    290    115      0      0      0      0      0      0      0      0      0
>Node 0, zone   Normal    304    540    116     13      2      2      0      0      0      0      0
>=========================
>             total      
used       free     shared    buffers     cached
>Mem:           497        487         10          0         63        303
>-/+ buffers/cache:        120        376
>Swap:         1458         34       1424
>Total:        1956        522       1434
>=========================
>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      DMA      6      6      7      8     10      9      7      4      1      0      0
>Node 0, zone   Normal   2129   2612   2166   1723   1260    759    359    108     10      0      0
>=========================
>             total      
used       free     shared    buffers     cached
>Mem:           497         47        449          0          0          5
>-/+ buffers/cache:         41        455
>Swap:         1458         97       1361
>Total:        1956        145       1811
>=========================
>
>
>It was verified using a sample shell script "reclaim_memory.sh" which keeps recovering memory by doing "echo 500 > /dev/shrinkmem" until no further reclaim is possible.
>
>
>The experiments were performed with various scenarios as follows:
>a) Just after the boot up - (could recover around 150MB with 512MB RAM)
>b) After running many applications 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 playing - (Not applications killed)
>
>d) revoke all background applications again, after running reclaim - (No impact, normal behavior)
>   [Just it took little extra time to launch, as if it was launched for first time]
>
>
>
>
>Please see more discussions on this in the last year mailing list:
>
>https://lkml.org/lkml/2012/4/15/35
>
>
>
>Thank You!
>With regards,
>Pintu Kumar
>Samsung - India
>
>
>
>
>
>