Hi,
I have been reading the Je source code, and I have some question about the
purging order.
The fisrt one is , according to the code comments, the clean-dirty
fragmentation is measured as,
* Order such that chunks with higher fragmentation are "less than"
* those with lower fragmentation -- purging order is from "least" to
* "greatest".
mean current avail run size nruns_avail-nruns_adjac
-------------------------------------------- =
----------------------------------
mean defragmented avail run size nruns_avail
So if I have a chunkA with avail_runs = 10, adjac = 1, and another chunkB with
avail_runs = 20, adjac = 5.
Obviously, the fragmentA(0.9) > fragmentB(0.75), so the A will be prior to B in
the dirty chunk tree, and
will be purged first. But the chunkB truely has more adjacs than the A, and the
performace gain after purging
chunkA is also less than the other(0.1 vs 0.25). Why we prefer to purge the
chunk with "less adjacs"?
Shouldn't we purge more adjacs or clean-dirty fragments to acquire more
continuous unalloc pages?
Another question is, I notice that before the git node e3d13060 there are two
avail-trees, one is for dirty,
and another for clean,
arena_avail_tree_t runs_avail_clean;
arena_avail_tree_t runs_avail_dirty;
After that, the two became one. So how to ensure the new runs allocaction to
prefer to dirty pages?
Is the modification will cause more performance regression than before?
That's all, thanks.
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