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37 lines
1.2 KiB
C
37 lines
1.2 KiB
C
#pragma once
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#include <cstdio>
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#include <cstdlib>
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#include <sys/types.h>
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#if defined(__linux__)
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#include <fcntl.h>
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#endif
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// Bounded write-behind for loggerd's append-only FILE* (rlog/qlog/video): async
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// writeback of new bytes (sync_file_range) + drop the now-clean prior range
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// (posix_fadvise DONTNEED) so dirty pages don't pile up and force reclaim stalls.
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// Never fsyncs, never drops dirty pages. Linux-only, no-op elsewhere, best-effort.
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// Disable: LOGGERD_NO_WRITEBACK_TUNING=1. synced/dropped are caller-owned cursors.
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static inline void stream_writeback(FILE *f, off_t &synced, off_t &dropped,
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off_t chunk = (off_t)4 << 20) {
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#if defined(__linux__)
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static const bool disabled = getenv("LOGGERD_NO_WRITEBACK_TUNING") != nullptr;
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if (disabled || f == nullptr) return;
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off_t pos = ftello(f);
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if (pos < 0 || pos - synced < chunk) return;
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if (fflush(f) != 0) return;
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int fd = fileno(f);
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sync_file_range(fd, synced, pos - synced, SYNC_FILE_RANGE_WRITE);
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if (synced > dropped) {
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posix_fadvise(fd, dropped, synced - dropped, POSIX_FADV_DONTNEED);
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dropped = synced;
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}
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synced = pos;
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#else
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(void)f; (void)synced; (void)dropped; (void)chunk;
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#endif
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}
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