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Improve size class header

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Mainly fixing typos.  The only non-trivial change is in the
computation for SC_NPSIZES, though the result wouldn't be any
different when SC_NGROUP = 4 as is always the case at the moment.
This commit is contained in:
Yinan Zhang 2019-04-18 15:11:07 -07:00 committed by Qi Wang
parent 702d76dbd0
commit ae124b8684
1 changed files with 21 additions and 8 deletions
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27
include/jemalloc/internal/sc.h
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@ -18,7 +18,7 @@
* each one covers allocations for base / SC_NGROUP possible allocation sizes.
* We call that value (base / SC_NGROUP) the delta of the group. Each size class
* is delta larger than the one before it (including the initial size class in a
* group, which is delta large than 2**base, the largest size class in the
* group, which is delta larger than base, the largest size class in the
* previous group).
* To make the math all work out nicely, we require that SC_NGROUP is a power of
* two, and define it in terms of SC_LG_NGROUP. We'll often talk in terms of
@ -53,10 +53,11 @@
* classes; one per power of two, up until we hit the quantum size. There are
* therefore LG_QUANTUM - SC_LG_TINY_MIN such size classes.
*
* Next, we have a size class of size LG_QUANTUM. This can't be the start of a
* group in the sense we described above (covering a power of two range) since,
* if we divided into it to pick a value of delta, we'd get a delta smaller than
* (1 << LG_QUANTUM) for sizes >= (1 << LG_QUANTUM), which is against the rules.
* Next, we have a size class of size (1 << LG_QUANTUM). This can't be the
* start of a group in the sense we described above (covering a power of two
* range) since, if we divided into it to pick a value of delta, we'd get a
* delta smaller than (1 << LG_QUANTUM) for sizes >= (1 << LG_QUANTUM), which
* is against the rules.
*
* The first base we can divide by SC_NGROUP while still being at least
* (1 << LG_QUANTUM) is SC_NGROUP * (1 << LG_QUANTUM). We can get there by
@ -206,8 +207,20 @@
- SC_NPSEUDO \
/* And the tiny group. */ \
- SC_NTINY \
/* Groups where ndelta*delta is not a multiple of the page size. */ \
- (2 * (SC_NGROUP)))
/* Sizes where ndelta*delta is not a multiple of the page size. */ \
- (SC_LG_NGROUP * SC_NGROUP))
/*
* Note that the last line is computed as the sum of the second column in the
* following table:
* lg(base) | count of sizes to exclude
* ------------------------------|-----------------------------
* LG_PAGE - 1 | SC_NGROUP - 1
* LG_PAGE | SC_NGROUP - 1
* LG_PAGE + 1 | SC_NGROUP - 2
* LG_PAGE + 2 | SC_NGROUP - 4
* ... | ...
* LG_PAGE + (SC_LG_NGROUP - 1) | SC_NGROUP - (SC_NGROUP / 2)
*/
/*
* We declare a size class is binnable if size < page size * group. Or, in other