On Sunday 13 January 2013 16:32:57 PINTU KUMAR wrote:
> 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.
Could you please post the code somewhere so it can be reviewed?
Thanks,
--
Bartlomiej Zolnierkiewicz
Samsung Poland R&D Center
> 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
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