From 2bb89b7f114e4beb3012f63e12e726ae23005e6f Mon Sep 17 00:00:00 2001 From: Samuel Williams Date: Fri, 4 Nov 2022 20:13:48 +1300 Subject: [PATCH] Lower priority of `POSIX_MADV_DONTNEED`. (#6671) --- cont.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) diff --git a/cont.c b/cont.c index 635faf8809..a85b7fc2d1 100644 --- a/cont.c +++ b/cont.c @@ -693,21 +693,36 @@ fiber_pool_stack_free(struct fiber_pool_stack * stack) if (DEBUG) fprintf(stderr, "fiber_pool_stack_free: %p+%"PRIuSIZE" [base=%p, size=%"PRIuSIZE"]\n", base, size, stack->base, stack->size); -#if VM_CHECK_MODE > 0 && defined(MADV_DONTNEED) + // The pages being used by the stack can be returned back to the system. + // That doesn't change the page mapping, but it does allow the system to + // reclaim the physical memory. + // Since we no longer care about the data itself, we don't need to page + // out to disk, since that is costly. Not all systems support that, so + // we try our best to select the most efficient implementation. + // In addition, it's actually slightly desirable to not do anything here, + // but that results in higher memory usage. + +#ifdef __wasi__ + // WebAssembly doesn't support madvise, so we just don't do anything. +#elif VM_CHECK_MODE > 0 && defined(MADV_DONTNEED) // This immediately discards the pages and the memory is reset to zero. madvise(base, size, MADV_DONTNEED); -#elif defined(POSIX_MADV_DONTNEED) - posix_madvise(base, size, POSIX_MADV_DONTNEED); #elif defined(MADV_FREE_REUSABLE) + // Darwin / macOS / iOS. // Acknowledge the kernel down to the task info api we make this // page reusable for future use. // As for MADV_FREE_REUSE below we ensure in the rare occasions the task was not // completed at the time of the call to re-iterate. while (madvise(base, size, MADV_FREE_REUSABLE) == -1 && errno == EAGAIN); #elif defined(MADV_FREE) + // Recent Linux. madvise(base, size, MADV_FREE); #elif defined(MADV_DONTNEED) + // Old Linux. madvise(base, size, MADV_DONTNEED); +#elif defined(POSIX_MADV_DONTNEED) + // Solaris? + posix_madvise(base, size, POSIX_MADV_DONTNEED); #elif defined(_WIN32) VirtualAlloc(base, size, MEM_RESET, PAGE_READWRITE); // Not available in all versions of Windows.