Hi Johannes, On Thu, Oct 22, 2015 at 12:21:28AM -0400, Johannes Weiner wrote: ... > Patch #5 adds accounting and tracking of socket memory to the unified > hierarchy memory controller, as described above. It uses the existing > per-cpu charge caches and triggers high limit reclaim asynchroneously. > > Patch #8 uses the vmpressure extension to equalize pressure between > the pages tracked natively by the VM and socket buffer pages. As the > pool is shared, it makes sense that while natively tracked pages are > under duress the network transmit windows are also not increased. First of all, I've no experience in networking, so I'm likely to be mistaken. Nevertheless I beg to disagree that this patch set is a step in the right direction. Here goes why. I admit that your idea to get rid of explicit tcp window control knobs and size it dynamically basing on memory pressure instead does sound tempting, but I don't think it'd always work. The problem is that in contrast to, say, dcache, we can't shrink tcp buffers AFAIU, we can only stop growing them. Now suppose a system hasn't experienced memory pressure for a while. If we don't have explicit tcp window limit, tcp buffers on such a system might have eaten almost all available memory (because of network load/problems). If a user workload that needs a significant amount of memory is started suddenly then, the network code will receive a notification and surely stop growing buffers, but all those buffers accumulated won't disappear instantly. As a result, the workload might be unable to find enough free memory and have no choice but invoke OOM killer. This looks unexpected from the user POV. That said, I think we do need per memcg tcp window control similar to what we have system-wide. In other words, Glauber's work makes sense to me. You might want to point me at my RFC patch where I proposed to revert it (https://lkml.org/lkml/2014/9/12/401). Well, I've changed my mind since then. Now I think I was mistaken, luckily I was stopped. However, I may be mistaken again :-) Thanks, Vladimir -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
