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cache: Only start at high watermark (#10403)

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Currently, cache purges are triggered as soon as the low watermark is exceeded.
To reduce IO this should only be done when reaching the high watermark.
This simplifies checks and reduces all calls for a GC to go through
`dcache.diskSpaceAvailable(size)`. While a comment claims that 
`dcache.triggerGC <- struct{}{}` was non-blocking I don't see how 
that was possible. Instead, we add a 1 size to the queue channel 
and use channel  semantics to avoid blocking when a GC has 
already been requested.

`bytesToClear` now takes the high watermark into account to it will 
not request any bytes to be cleared until that is reached.
This commit is contained in:
Klaus Post
2020-09-02 17:48:44 -07:00
committed by GitHub
parent d08b4b147d
commit 650dccfa9e
5 changed files with 69 additions and 54 deletions
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30
cmd/disk-cache-utils_test.go
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@@ -149,22 +149,26 @@ func TestNewFileScorer(t *testing.T) {
}
func TestBytesToClear(t *testing.T) {
testCases := []struct {
total int64
free int64
quotaPct uint64
watermarkLow uint64
expected uint64
total int64
free int64
quotaPct uint64
watermarkLow uint64
watermarkHigh uint64
expected uint64
}{
{1000, 800, 40, 90, 0},
{1000, 200, 40, 90, 400},
{1000, 400, 40, 90, 240},
{1000, 600, 40, 90, 40},
{1000, 600, 40, 70, 120},
{1000, 1000, 90, 70, 0},
{1000, 0, 90, 70, 370},
{total: 1000, free: 800, quotaPct: 40, watermarkLow: 90, watermarkHigh: 90, expected: 0},
{total: 1000, free: 200, quotaPct: 40, watermarkLow: 90, watermarkHigh: 90, expected: 400},
{total: 1000, free: 400, quotaPct: 40, watermarkLow: 90, watermarkHigh: 90, expected: 240},
{total: 1000, free: 600, quotaPct: 40, watermarkLow: 90, watermarkHigh: 90, expected: 40},
{total: 1000, free: 600, quotaPct: 40, watermarkLow: 70, watermarkHigh: 70, expected: 120},
{total: 1000, free: 1000, quotaPct: 90, watermarkLow: 70, watermarkHigh: 70, expected: 0},
// High not yet reached..
{total: 1000, free: 250, quotaPct: 100, watermarkLow: 50, watermarkHigh: 90, expected: 0},
{total: 1000, free: 250, quotaPct: 100, watermarkLow: 50, watermarkHigh: 90, expected: 0},
}
for i, tc := range testCases {
toClear := bytesToClear(tc.total, tc.free, tc.quotaPct, tc.watermarkLow)
toClear := bytesToClear(tc.total, tc.free, tc.quotaPct, tc.watermarkLow, tc.watermarkHigh)
if tc.expected != toClear {
t.Errorf("test %d expected %v, got %v", i, tc.expected, toClear)
}