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. 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>