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HPCC-32912 Ensure the row manager peak pages is updated correctly #19251

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merged 1 commit into from
Nov 4, 2024
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HPCC-32912 Ensure the row manager peak pages is updated correctly #19251

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21 changes: 16 additions & 5 deletions roxie/roxiemem/roxiemem.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5155,18 +5155,23 @@ class CChunkingRowManager : public CRowManager
unsigned pageLimit = getPageLimit();
if (totalPages <= pageLimit)
{
unsigned newHeapPages;
if (pageLimit != UNLIMITED_PAGES)
{
//Use compare_exchange so that only one thread can increase the number of pages at a time.
//(Don't use atomic_add because we need to check the limit hasn't been exceeded.)
if (!totalHeapPages.compare_exchange_weak(numHeapPages, numHeapPages + numRequested, std::memory_order_relaxed))
newHeapPages = numHeapPages + numRequested;
if (!totalHeapPages.compare_exchange_weak(numHeapPages, newHeapPages, std::memory_order_relaxed))
continue;
}
else
{
//Unlimited pages => just increment the total
totalHeapPages.fetch_add(numRequested, std::memory_order_relaxed);
newHeapPages = totalHeapPages.fetch_add(numRequested, std::memory_order_relaxed) + numRequested;
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This is a fetch_add(), should we be adding numRequested twice ?

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ok, no, its correct as is. fetch_add() returns value before increment

}

//Ensure the total is correct if two threads allocate big blocks of memory at the same time
totalPages = dataBuffPages + newHeapPages;
break;
}

Expand Down Expand Up @@ -5203,9 +5208,15 @@ class CChunkingRowManager : public CRowManager

if (totalPages > peakPages)
{
if (trackMemoryByActivity)
getPeakActivityUsage();
peakPages = totalPages;
unsigned value = totalPages;
//Atomically update the peak - this could temporarily reduce the value, but it will eventually be correct.
while (value > peakPages.load())
value = peakPages.exchange(value, std::memory_order_acq_rel);

//Check if this thread actually updated the peak value - or did another thread beat us to it.
if (totalPages == peakPages)
if (trackMemoryByActivity)
getPeakActivityUsage();
}
return totalPages;
}
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