Use CLOCK_MONOTONIC for background thread sleep to prevent clock rollback stalls#4
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antonio2368 merged 3 commits intodevfrom Apr 2, 2026
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When CLOCK_MONOTONIC is available, use it for measuring sleep duration and initializing condvars instead of gettimeofday. This matches the condvar clock attribute set during init and avoids issues with wall clock adjustments (e.g. NTP corrections) affecting sleep calculations. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
azat
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Apr 1, 2026
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Good that we have CI for jemalloc! |
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Let's also send patch to upstream (whatever upstream repo is) |
…failure Replace duplicated clock_gettime/gettimeofday blocks with nstime_init_update() which already handles the monotonic vs realtime fallback. Add error handling for pthread_condattr_setclock: in postfork_child, fall back to default CLOCK_REALTIME attributes; in boot1, propagate the failure. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
azat
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Apr 2, 2026
azat
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Apr 2, 2026
In postfork_child, fall back to default condvar (CLOCK_REALTIME) if condattr_init fails. In boot1, return failure since initialization cannot proceed without a properly configured condvar. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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background_thread_sleep()computes thepthread_cond_timedwaitdeadline fromgettimeofday()(CLOCK_REALTIME). If the wall clock jumps backward (NTP correction, VMsnapshot, leap second), the deadline ends up far in the future and the background thread stops purging dirty pages — potentially for hours or days.
This was observed in production where NTP corrections caused unbounded RSS growth due to the background thread stalling.
Fix
clock_gettime(CLOCK_MONOTONIC)CLOCK_MONOTONICon the condvar viapthread_condattr_setclockat both init sites (background_thread_boot1andbackground_thread_postfork_child)CLOCK_MONOTONICretain the originalgettimeofdayfallback