Files
rippled/src/libxrpl/basics/MallocTrim.cpp
Valentin Balaschenko bdd106d992 Explicitly trim the heap after cache sweeps (#6022)
Limited to Linux/glibc builds.
2026-02-24 21:33:13 +00:00

158 lines
4.3 KiB
C++

#include <xrpl/basics/Log.h>
#include <xrpl/basics/MallocTrim.h>
#include <boost/predef.h>
#include <chrono>
#include <cstdint>
#include <cstdio>
#include <fstream>
#include <sstream>
#if defined(__GLIBC__) && BOOST_OS_LINUX
#include <sys/resource.h>
#include <malloc.h>
#include <unistd.h>
// Require RUSAGE_THREAD for thread-scoped page fault tracking
#ifndef RUSAGE_THREAD
#error "MallocTrim rusage instrumentation requires RUSAGE_THREAD on Linux/glibc"
#endif
namespace {
bool
getRusageThread(struct rusage& ru)
{
return ::getrusage(RUSAGE_THREAD, &ru) == 0; // LCOV_EXCL_LINE
}
} // namespace
#endif
namespace xrpl {
namespace detail {
// cSpell:ignore statm
#if defined(__GLIBC__) && BOOST_OS_LINUX
inline int
mallocTrimWithPad(std::size_t padBytes)
{
return ::malloc_trim(padBytes);
}
long
parseStatmRSSkB(std::string const& statm)
{
// /proc/self/statm format: size resident shared text lib data dt
// We want the second field (resident) which is in pages
std::istringstream iss(statm);
long size, resident;
if (!(iss >> size >> resident))
return -1;
// Convert pages to KB
long const pageSize = ::sysconf(_SC_PAGESIZE);
if (pageSize <= 0)
return -1;
return (resident * pageSize) / 1024;
}
#endif // __GLIBC__ && BOOST_OS_LINUX
} // namespace detail
MallocTrimReport
mallocTrim(std::string_view tag, beast::Journal journal)
{
// LCOV_EXCL_START
MallocTrimReport report;
#if !(defined(__GLIBC__) && BOOST_OS_LINUX)
JLOG(journal.debug()) << "malloc_trim not supported on this platform (tag=" << tag << ")";
#else
// Keep glibc malloc_trim padding at 0 (default): 12h Mainnet tests across 0/256KB/1MB/16MB
// showed no clear, consistent benefit from custom padding—0 provided the best overall balance
// of RSS reduction and trim-latency stability without adding a tuning surface.
constexpr std::size_t TRIM_PAD = 0;
report.supported = true;
if (journal.debug())
{
auto readFile = [](std::string const& path) -> std::string {
std::ifstream ifs(path, std::ios::in | std::ios::binary);
if (!ifs.is_open())
return {};
// /proc files are often not seekable; read as a stream.
std::ostringstream oss;
oss << ifs.rdbuf();
return oss.str();
};
std::string const tagStr{tag};
std::string const statmPath = "/proc/self/statm";
auto const statmBefore = readFile(statmPath);
long const rssBeforeKB = detail::parseStatmRSSkB(statmBefore);
struct rusage ru0{};
bool const have_ru0 = getRusageThread(ru0);
auto const t0 = std::chrono::steady_clock::now();
report.trimResult = detail::mallocTrimWithPad(TRIM_PAD);
auto const t1 = std::chrono::steady_clock::now();
struct rusage ru1{};
bool const have_ru1 = getRusageThread(ru1);
auto const statmAfter = readFile(statmPath);
long const rssAfterKB = detail::parseStatmRSSkB(statmAfter);
// Populate report fields
report.rssBeforeKB = rssBeforeKB;
report.rssAfterKB = rssAfterKB;
report.durationUs = std::chrono::duration_cast<std::chrono::microseconds>(t1 - t0);
if (have_ru0 && have_ru1)
{
report.minfltDelta = ru1.ru_minflt - ru0.ru_minflt;
report.majfltDelta = ru1.ru_majflt - ru0.ru_majflt;
}
std::int64_t const deltaKB = (rssBeforeKB < 0 || rssAfterKB < 0)
? 0
: (static_cast<std::int64_t>(rssAfterKB) - static_cast<std::int64_t>(rssBeforeKB));
JLOG(journal.debug()) << "malloc_trim tag=" << tagStr << " result=" << report.trimResult
<< " pad=" << TRIM_PAD << " bytes"
<< " rss_before=" << rssBeforeKB << "kB"
<< " rss_after=" << rssAfterKB << "kB"
<< " delta=" << deltaKB << "kB"
<< " duration_us=" << report.durationUs.count()
<< " minflt_delta=" << report.minfltDelta
<< " majflt_delta=" << report.majfltDelta;
}
else
{
report.trimResult = detail::mallocTrimWithPad(TRIM_PAD);
}
#endif
return report;
// LCOV_EXCL_STOP
}
} // namespace xrpl