On Sun, Apr 15, 2012 at 2:47 AM, PINTU KUMAR <pintu_agarwal@xxxxxxxxx> wrote: > Dear All, > > This is regarding a small proposal for shrink_all_memory( ) function which is found in mm/vmscan.c. > For those who are not aware, this function helps in reclaiming specified amount of physical memory and returns number of freed pages. > > Currently this function is under CONFIG_HIBERNATION flag, so cannot be used by others without enabling hibernation. > Moreover this function is not exported to the outside world, so no driver can use it directly without including EXPORT_SYMBOL(shrink_all_memory) and recompiling the kernel. > The purpose of using it under hibernation(kernel/power/snapshot.c) is to regain enough physical pages to create hibernation image. > > The same can be useful for some drivers who wants to allocate large contiguous memory (in MBs) but his/her system is in very bad state and could not do so without rebooting. > Due to this bad state of the system the user space application will be badly hurt on performance, and there could be a need to quickly reclaim all physical memory from user space. > This could be very helpful for small embedded products and smart phones where rebooting is never a preferred choice. > > With this support in kernel, a small utility can be developed in user space which user can run and reclaim as many physical pages and noticed that his system performance is increased without rebooting. > > To make this work, I have performed a sample experiment on my ubuntu(10.x) machine running with kernel-3.3.0. > > Also I performed the similar experiment of one of our Samsung smart phones as well. > > Following are the results from Ubuntu: > > 1) I downloaded kernel3.3.0 and made the respective changes in mm/vmscan.c. That is added EXPORT_SYMBOL(shrink_all_memory) under the function shrink_all_memory( ). > (Note: CONFIG_HIBERNATION was already enabled for my system.) > > 2) Then I build the kernel and installed it on my Ubuntu PC. > > 3) After that I have developed a small kernel module (miscdevice: /dev/shrinkmem) to call shrink_all_memory( ) under my driver write( ) function. > > 4) Then from user space I just need to do this: > > # echo 100 > /dev/shrinkmem (To reclaim 100MB of physical memory without reboot) > > > The results that were obtained with this experiment is as follows: > > 1) At some point of time, the buddyinfo and free pages on my Ubuntu were as follows: > root@pintu-ubuntu:~/PintuHomeTest/KERNEL_ORG# cat /proc/buddyinfo ; free -tmNode 0, zone DMA 468 23 0 0 0 0 0 0 0 0 0 > Node 0, zone Normal 898 161 38 8 0 0 0 0 0 0 0 > total used free shared buffers cached > Mem: 497 489 7 0 37 405 > -/+ buffers/cache: 47 449 > Swap: 1458 158 1300 > Total: 1956 648 1308 > > > 2) After doing "echo 100 > /dev/shrinkmem" : > [19653.833916] [SHRINKMEM]: memsize(in MB) = 100 > [19653.863618] <SHRINKMEM>: Number of Pages Freed: 26756 > [19653.863664] [SHRINKMEM] : Device is Closed.... > > Node 0, zone DMA 411 166 51 5 0 0 0 0 0 0 0 > Node 0, zone Normal 2915 3792 2475 1335 730 23 0 0 0 0 0 > total used free shared buffers cached > Mem: 497 323 173 0 37 238 > -/+ buffers/cache: 47 449 > Swap: 1458 158 1300 > Total: 1956 481 1474 > > > 3) After running again with : echo 512 > /dev/shrinkmem > [21961.064534] [SHRINKMEM]: memsize(in MB) = 512 > [21961.109497] <SHRINKMEM>: Number of Pages Freed: 61078 > [21961.109562] [SHRINKMEM] : Device is Closed.... > Node 0, zone DMA 116 99 87 58 16 6 1 0 0 0 0 > Node 0, zone Normal 6697 6939 5529 3756 1442 203 17 0 0 0 0 > total used free shared buffers cached > Mem: 497 87 410 0 37 9 > -/+ buffers/cache: 40 456 > Swap: 1458 158 1300 > Total: 1956 245 1711 > > > 4) Thus in both the cases huge number of free pages were reclaimed. > > 5) After running this on my system, the performance was improved quickly. > > 6) I performed the same experiment on our Samsung Smart phones as well. And I have seen a drastic improve in performance after running this for 3/4 times. > In case of phones it is more helpful as there is no swap space. > > 7) Your feedback and suggestion is important. Based on the feedback, I can plan to submit the patches officially after performing basic cleanups. > > > Future Work > ========== > Our final goal is to use it during lowmem notifier where shrink_all_memory will be called automatically in background if the memory pressure falls below certain limit defined by the system. > For example we can measure the percentage memory fragmentation level of the system across each zone and if the fragmentation percentage goes above say 80-85% during lowmem notifier, we can invoke shrink_all_memory() in background. Does it make sense to let kswapd reclaim pages at background w/ user configured watermark? --Ying > > This can be used by some application which requires large mmap or shared memory mapping. > > This can be even using inside the multimedia drivers that requires large contiguous memory to check if that many memory pages can be reclaimed or not. > > > Please provide your valuable feedback and suggestion. > > > Thank you very much ! > > > With Regards, > Pintu Kumar > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@xxxxxxxxx. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ > Don't email: <a hrefmailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a> -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . 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