moonchen commented on code in PR #13380:
URL: https://github.com/apache/trafficserver/pull/13380#discussion_r3915349507
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src/iocore/cache/RamCacheLRU.cc:
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@@ -213,6 +218,26 @@ RamCacheLRU::put(CryptoHash *key, IOBufferData *data,
[[maybe_unused]] uint32_t
if (e->auxkey == auxkey) {
lru.remove(e);
lru.enqueue(e);
+ if (copy) {
Review Comment:
Please guard this with `copy && !e->copy`.
When two requests both get a RAM-cache miss, both read the same object from
disk, and then both try to fill the RAM cache, whichever finishes first inserts
a private copy. The other request finds that entry resident and currently
allocates and copies the entire object again. Both requests allocate a
RAM-cache buffer, but only the first allocation is necessary.
If `e->copy` is already true, the stored buffer is private and `get()` never
exposes it directly, so replacing it is unnecessary. The guard preserves the
shared-to-private transition while avoiding the redundant allocation and
memcpy. The same applies to the corresponding resident-refresh block in S3-FIFO.
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