Andrew Piskorski wrote:
To reduce your RAM usage, you would definitely want to investigate
ttrace, included in the Tcl Threads Extension. However, you don't
seem to be running out memory, so this is unlikely to be that big a
help in your case.
I have had very little success in getting ttrace to work.
However, I was looking at the memory stats on mempools.adp and I noticed
that the overhead was in the neighborhood of 50%-60%. After a small
amount of looking, I realized this is entirely expected: the
USE_THREAD_ALLOC version of Tcl_Alloc is a power-of-2 allocator, meaning
that it rounds up all requests that it handles to the next higher power
of 2. So for example, a request to allocate 600 bytes will really
allocate 1024 bytes and the difference is wasted space. On average, you
would expect this wasted space to be about 50% more than you requested.
So, inspired by the description of google's tcmalloc which uses a large
number of buckets, I added a whole lot more buckets spaced closely
together (from 8 bytes for the smaller sizes to 512 bytes for larger
sizes) in tclThreadAlloc.c and the results were as I hoped; the memory
overhead went down to around 10%.
Adding all these extra buckets will impose some overhead of its own and
a small (probably unnoticable) performance impact, but the amount of
memory allocated seems to dwarf this overhead and real impact on memory
size is noticable. My server that would be around 90M a few minutes
after starting is now only 65-70M. On a memory-tight environment like a
unixshell.org setup, this can be quite significant.
On a larger server with more memory this can still matter: if trying to
keep the overall memory footprint small isn't really your issue then you
could think of it as being able to run 40% more threads.
-J
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