Bug #75368 [Com]: mmap/munmap trashing on unlucky allocations

Edit report at https://bugs.php.net/bug.php?id=75368&edit=1 ID: 75368 Comment by: spam2 at rhsoft dot net Reported by: nikic@php.net Summary: mmap/munmap trashing on unlucky allocations Status: Closed Type: Bug Package: Scripting Engine problem PHP Version: 7.0.24 Block user comment: N Private report: N New Comment: thank you! this seems to make a big difference for phpdoc on my workstation when the KDE session which seems to have small memory leaks is running a long time - phpdoc sometimes takes ages for no reason same run, only the php-cli binary changed while currently the memleak/fragmentation is not so high after 12 hours but a noticeable change 17/17 [============================] 100% 12.553s .. 17/17 [============================] 100% 6.488s .. Previous Comments: ------------------------------------------------------------------------ [2017-10-13 11:03:06] dmitry@php.net Automatic comment on behalf of dmitry@zend.com Revision: http://git.php.net/?p=php-src.git;a=commit;h=397f5cb687f4f31cb0dec85ba5a87237394ca12d Log: Fixed bug #75368 (mmap/munmap trashing on unlucky allocations) ------------------------------------------------------------------------ [2017-10-13 06:46:34] laruence@php.net it may still be triggered by i = 94 * 2 if you cache one chunk ------------------------------------------------------------------------ [2017-10-12 19:53:59] nikic@php.net Description: ------------ It may happen that memory is allocated and freed in such a way that the allocation mmaps a new ZMM chunk and the deallocation immediately unmaps it again. The attached script demonstrates this issues. It will execute quickly up to a certain point (for me on master i=94) and then hang for a while. strace shows that during this time a sequence of mmap, madvise and munmap is repeated many times: mmap(NULL, 2097152, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7f3927400000 madvise(0x7f3927400000, 2097152, MADV_HUGEPAGE) = 0 munmap(0x7f3927400000, 2097152) = 0 This issue may be fixed by ensuring we always cache at least one chunk. Test script: --------------- <?php $bigArray = range(0, 256 * 1024 - 1); var_dump(memory_get_usage(true) / (1024*1024)); $array = []; for ($i = 0; $i < 1024; $i++) { echo "$i\n"; $array[] = range(0, 1023); for ($j = 0; $j < 16 * 1024; $j++) { $x = range(0, 1023); unset($x); } } ------------------------------------------------------------------------ -- Edit this bug report at https://bugs.php.net/bug.php?id=75368&edit=1