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8247358: Shenandoah: reconsider free budget slice for marking
Reviewed-by: zgu
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shipilev committed Jun 11, 2020
1 parent 7da56df commit 9ac1ab372d74d6007ab30fb997c72cb04a7076e6
Showing 1 changed file with 4 additions and 8 deletions.
@@ -50,12 +50,8 @@
* notion of progress is clear: we get reported the "used" size from the processed regions
* and use the global heap-used as the baseline.
*
* The allocatable space when GC is running is "free" at the start of cycle, but the
* The allocatable space when GC is running is "free" at the start of phase, but the
* accounted budget is based on "used". So, we need to adjust the tax knowing that.
* Also, since we effectively count the used space three times (mark, evac, update-refs),
* we need to multiply the tax by 3. Example: for 10 MB free and 90 MB used, GC would
* come back with 3*90 MB budget, and thus for each 1 MB of allocation, we have to pay
* 3*90 / 10 MBs. In the end, we would pay back the entire budget.
*/

void ShenandoahPacer::setup_for_mark() {
@@ -68,7 +64,7 @@ void ShenandoahPacer::setup_for_mark() {
size_t taxable = free - non_taxable;

double tax = 1.0 * live / taxable; // base tax for available free space
tax *= 3; // mark is phase 1 of 3, claim 1/3 of free for it
tax *= 1; // mark can succeed with immediate garbage, claim all available space
tax *= ShenandoahPacingSurcharge; // additional surcharge to help unclutter heap

restart_with(non_taxable, tax);
@@ -91,7 +87,7 @@ void ShenandoahPacer::setup_for_evac() {
size_t taxable = free - non_taxable;

double tax = 1.0 * used / taxable; // base tax for available free space
tax *= 2; // evac is phase 2 of 3, claim 1/2 of remaining free
tax *= 2; // evac is followed by update-refs, claim 1/2 of remaining free
tax = MAX2<double>(1, tax); // never allocate more than GC processes during the phase
tax *= ShenandoahPacingSurcharge; // additional surcharge to help unclutter heap

@@ -115,7 +111,7 @@ void ShenandoahPacer::setup_for_updaterefs() {
size_t taxable = free - non_taxable;

double tax = 1.0 * used / taxable; // base tax for available free space
tax *= 1; // update-refs is phase 3 of 3, claim the remaining free
tax *= 1; // update-refs is the last phase, claim the remaining free
tax = MAX2<double>(1, tax); // never allocate more than GC processes during the phase
tax *= ShenandoahPacingSurcharge; // additional surcharge to help unclutter heap

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