Hi Alexey, a modern OS won't give you a physical address. Instead you get virtual memory which allows the OS to support features like defragmentation. "fine-grained per-entry" sounds like a byte-array for every entry. We tested something like that and the result is again higher GC pauses. In our case a FGC with off-heap caches takes e.g. up to 1s. With the same data and using on-heap caches it takes up to 25s. With a byte-array per entry we get about 4s for a FGC. With some optimizations you might get down a bit, however, in view of the FGC time I fear that such an approach causes a significant impact for applications which need to keep huge caches.
Kind regards, Peter 2017-01-26 15:57 GMT+01:00 Alexey Goncharuk <alexey.goncha...@gmail.com>: > Hi Peter, > > Leaving defragmentation to Ignite is one of the reasons we are trying > PageMemory approach. In Ignite 1.x we basically use OS memory allocator to > place a value off-heap. Once the OS has given us a pointer, the memory > cannot be moved around unless we free this region, thus the fragmentation. > On the other hand, with PageMemory approach we can define the page layout > ourselves and, given fine-grained per-entry locking, move values around in > memory. This makes memory management more complicated and usually defines > some restrictions on the data structures, but we expect this will give us > more control over the data. > > For example, one of the tricks we can do in the future is cluster-wide > cache snapshots: we simply dump the continuous region of memory on disk and > get a node-local caches snapshot. This is impossible to do using current > off-heap approach. > > --AG > > 2017-01-25 12:32 GMT+03:00 Peter Schmitt <peter.schmitt....@gmail.com>: > >> Hi Val, >> >> fair enough :-) >> However, in the source-code it looks like "Flexible and precise >> per-cache memory limit" is supported already. >> At least each GridUnsafeMemory instance (in each GridCacheContext) >> receives the value from CacheConfiguration.getOffHeapMaxMemory). >> I haven't debugged it, but the instances are created per cache. >> >> Furthermore, I'm not sure about the memory-page concept, because you >> would get pages on top of pages (used by a modern OS). >> Sounds like even more fragmentation and in this case Ignite would need to >> do the defragmentation. >> >> Kind regards, >> Peter >> >> >> >> 2017-01-25 1:56 GMT+01:00 vkulichenko <valentin.kuliche...@gmail.com>: >> >>> I don't think I will be able to explain better than it's done in the >>> ticket >>> :) Current approach is naive and not always effective for multiple >>> reasons. >>> >>> -Val >>> >>> >>> >>> -- >>> View this message in context: http://apache-ignite-users.705 >>> 18.x6.nabble.com/OFFHEAP-TIERED-and-memory-fragmentation-tp1 >>> 0218p10235.html >>> Sent from the Apache Ignite Users mailing list archive at Nabble.com. >>> >> >> >
