From ba8f3587f55667c688acd7c5103c870983e294dd Mon Sep 17 00:00:00 2001 From: Lin Feng Date: Mon, 14 Dec 2020 19:11:19 -0800 Subject: init/main: fix broken buffer_init when DEFERRED_STRUCT_PAGE_INIT set In the booting phase if CONFIG_DEFERRED_STRUCT_PAGE_INIT is set, we have following callchain: start_kernel ... mm_init mem_init memblock_free_all reset_all_zones_managed_pages free_low_memory_core_early ... buffer_init nr_free_buffer_pages zone->managed_pages ... rest_init kernel_init kernel_init_freeable page_alloc_init_late kthread_run(deferred_init_memmap, NODE_DATA(nid), "pgdatinit%d", nid); wait_for_completion(&pgdat_init_all_done_comp); ... files_maxfiles_init It's clear that buffer_init depends on zone->managed_pages, but it's reset in reset_all_zones_managed_pages after that pages are readded into zone->managed_pages, but when buffer_init runs this process is half done and most of them will finally be added till deferred_init_memmap done. In large memory couting of nr_free_buffer_pages drifts too much, also drifting from kernels to kernels on same hardware. Fix is simple, it delays buffer_init run till deferred_init_memmap all done. But as corrected by this patch, max_buffer_heads becomes very large, the value is roughly as many as 4 times of totalram_pages, formula: max_buffer_heads = nrpages * (10%) * (PAGE_SIZE / sizeof(struct buffer_head)); Say in a 64GB memory box we have 16777216 pages, then max_buffer_heads turns out to be roughly 67,108,864. In common cases, should a buffer_head be mapped to one page/block(4KB)? So max_buffer_heads never exceeds totalram_pages. IMO it's likely to make buffer_heads_over_limit bool value alwasy false, then make codes 'if (buffer_heads_over_limit)' test in vmscan unnecessary. So this patch will change the original behavior related to buffer_heads_over_limit in vmscan since we used a half done value of zone->managed_pages before, or should we use a smaller factor(<10%) in previous formula. akpm: I think this is OK - the max_buffer_heads code is only needed on highmem machines, to prevent ZONE_NORMAL from being consumed by large amounts of buffer_heads attached to highmem pagecache. This problem will not occur on 64-bit machines, so this feature's non-functionality on such machines is a feature, not a bug. Link: https://lkml.kernel.org/r/20201123110500.103523-1-linf@wangsu.com Signed-off-by: Lin Feng Acked-by: Vlastimil Babka Cc: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- init/main.c | 2 -- 1 file changed, 2 deletions(-) (limited to 'init') diff --git a/init/main.c b/init/main.c index 82ae0d1345a0..404366e1a64d 100644 --- a/init/main.c +++ b/init/main.c @@ -58,7 +58,6 @@ #include #include #include -#include #include #include #include @@ -1036,7 +1035,6 @@ asmlinkage __visible void __init __no_sanitize_address start_kernel(void) fork_init(); proc_caches_init(); uts_ns_init(); - buffer_init(); key_init(); security_init(); dbg_late_init(); -- cgit v1.2.3