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This can take up a good >> amount of time for larger page sizes (e.g. around 40 >> milliseconds for a 1G page on a recent AMD-based system). >> >> This normally isn't a problem, since hugetlb pages are typically >> mapped by the application for a long time, and the initial >> delay when touching them isn't much of an issue. >> >> However, there are some use cases where a large number of hugetlb >> pages are touched when an application (such as a VM backed by these >> pages) starts. For 256 1G pages and 40ms per page, this would take >> 10 seconds, a noticeable delay. > > The current huge page zeroing code is not that great to begin with. Yeah definitely suboptimal. The current huge page zeroing code is both slow and it trashes the cache while zeroing. > There was a patchset posted some time ago to remedy at least some of it: > https://lore.kernel.org/all/20230830184958.2333078-1-ankur.a.arora@oracle.com/ > > but it apparently fell through the cracks. As Joao mentioned that got side tracked due to the preempt-lazy stuff. Now that lazy is in, I plan to follow up on the zeroing work. > Any games with "background zeroing" are notoriously crappy and I would > argue one should exhaust other avenues before going there -- at the end > of the day the cost of zeroing will have to get paid. Yeah and the background zeroing has dual cost: the cost in CPU time plus the indirect cost to other processes due to the trashing of L3 etc. Ankur