Ok, picked up the bait. This is on a system with Intel(R) Core(TM)2 Quad CPU Q9550 @ 2.83GHz 4×5666.59 bogomips Linux meerkat 2.6.35-28-generic-pae #50-Ubuntu SMP Fri Mar 18 20:43:15 UTC 2011 i686 GNU/Linux gcc version 4.4.5 total used free shared buffers cached Mem: 8127172 4220560 3906612 0 374328 2748796 -/+ buffers/cache: 1097436 7029736 Swap: 0 … Read more
You know, I somewhat doubt the memory profiler here. The memory management system in .NET actually tries to defragment the heap for you by moving around memory (that’s why you need to pin memory for it to be shared with an external DLL). Large memory allocations taken over longer periods of time is prone to … Read more
External fragmentation Total memory space is enough to satisfy a request or to reside a process in it, but it is not contiguous so it can not be used. Internal fragmentation Memory block assigned to process is bigger. Some portion of memory is left unused as it can not be used by another process.
I thought I’d put an answer with my observations because there are a lot of comments. Based off of your output at https://gist.github.com/christian-marie/7bc845d2da7847534104 We can determine the following: The GFP_MASK for the memory allocation tried is allowed to do the following. Can access emergency pools (I think this means access data below the high watermark … Read more
I think this article gives an excellent overview of defragmentation of SAN drives http://www.las-solanas.com/storage_virtualization/san_volume_defragmentation.php Basic points is that defragmenting is not recommended on SAN storage because it is difficult to correlate the physical location of blocks on the disk when the location has been virtualized by the SAN when presenting the LUN. If you were … Read more
I am answering to the linux tag. My answer is specific only to Linux. Yes, huge pages are more prone to fragmentation. There are two views of memory, the one your process gets (virtual) and the one the kernel manages (real). The larger any page, the more difficult it’s going to be to group (and … Read more
Imagine that you have a “large” (32 bytes) expanse of free memory: ———————————- | | ———————————- Now, allocate some of it (5 allocations): ———————————- |aaaabbccccccddeeee | ———————————- Now, free the first four allocations but not the fifth: ———————————- | eeee | ———————————- Now, try to allocate 16 bytes. Oops, I can’t, even though there’s nearly … Read more