On Thu, Nov 29, 2012 at 11:31 AM, Luigi Semenzato <semenzato@xxxxxxxxxx> wrote: > Oh well, I found the problem, it's laptop_mode. We keep it on by > default. When I turn it off, I can allocate as fast as I can, and no > OOMs happen until swap is exhausted. > > I don't think this is a desirable behavior even for laptop_mode, so if > anybody wants to help me debug it (or wants my help in debugging it) > do let me know. > Luigi, I thought we disabled Laptop mode a few weeks ago -- due to undesirable behavior with respect to too many writes happening. Are you sure it's on? > Thanks! > Luigi > > On Thu, Nov 29, 2012 at 10:46 AM, Luigi Semenzato <semenzato@xxxxxxxxxx> wrote: >> Minchan: >> >> I tried your suggestion to move the call to wake_all_kswapd from after >> "restart:" to after "rebalance:". The behavior is still similar, but >> slightly improved. Here's what I see. >> >> Allocating as fast as I can: 1.5 GB of the 3 GB of zram swap are used, >> then OOM kills happen, and the system ends up with 1 GB swap used, 2 >> unused. >> >> Allocating 10 MB/s: some kills happen when only 1 to 1.5 GB are used, >> and continue happening while swap fills up. Eventually swap fills up >> completely. This is better than before (could not go past about 1 GB >> of swap used), but there are too many kills too early. I would like >> to see no OOM kills until swap is full or almost full. >> >> Allocating 20 MB/s: almost as good as with 10 MB/s, but more kills >> happen earlier, and not all swap space is used (400 MB free at the >> end). >> >> This is with 200 processes using 20 MB each, and 2:1 compression ratio. >> >> So it looks like kswapd is still not aggressive enough in pushing >> pages out. What's the best way of changing that? Play around with >> the watermarks? >> >> Incidentally, I also tried removing the min_filelist_kbytes hacky >> patch, but, as usual, the system thrashes so badly that it's >> impossible to complete any experiment. I set it to a lower minimum >> amount of free file pages, 10 MB instead of the 50 MB which we use >> normally, and I could run with some thrashing, but I got the same >> results. >> >> Thanks! >> Luigi >> >> >> On Wed, Nov 28, 2012 at 4:31 PM, Luigi Semenzato <semenzato@xxxxxxxxxx> wrote: >>> I am beginning to understand why zram appears to work fine on our x86 >>> systems but not on our ARM systems. The bottom line is that swapping >>> doesn't work as I would expect when allocation is "too fast". >>> >>> In one of my tests, opening 50 tabs simultaneously in a Chrome browser >>> on devices with 2 GB of RAM and a zram-disk of 3 GB (uncompressed), I >>> was observing that on the x86 device all of the zram swap space was >>> used before OOM kills happened, but on the ARM device I would see OOM >>> kills when only about 1 GB (out of 3) was swapped out. >>> >>> I wrote a simple program to understand this behavior. The program >>> (called "hog") allocates memory and fills it with a mix of >>> incompressible data (from /dev/urandom) and highly compressible data >>> (1's, just to avoid zero pages) in a given ratio. The memory is never >>> touched again. >>> >>> It turns out that if I don't limit the allocation speed, I see >>> premature OOM kills also on the x86 device. If I limit the allocation >>> to 10 MB/s, the premature OOM kills stop happening on the x86 device, >>> but still happen on the ARM device. If I further limit the allocation >>> speed to 5 Mb/s, the premature OOM kills disappear also from the ARM >>> device. >>> >>> I have noticed a few time constants in the MM whose value is not well >>> explained, and I am wondering if the code is tuned for some ideal >>> system that doesn't behave like ours (considering, for instance, that >>> zram is much faster than swapping to a disk device, but it also uses >>> more CPU). If this is plausible, I am wondering if anybody has >>> suggestions for changes that I could try out to obtain a better >>> behavior with a higher allocation speed. >>> >>> Thanks! >>> Luigi -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>