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authorLin Feng <linf@wangsu.com>2020-12-14 19:11:19 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2020-12-15 12:13:44 -0800
commitba8f3587f55667c688acd7c5103c870983e294dd (patch)
tree9a7913caeed27034df2e6019dcf20655aa0b714c /init
parent862b6dee20b0db2ebaa728c302a1b296ff144de3 (diff)
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 <linf@wangsu.com> Acked-by: Vlastimil Babka <vbabka@suse.cz> Cc: Mel Gorman <mgorman@techsingularity.net> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'init')
-rw-r--r--init/main.c2
1 files changed, 0 insertions, 2 deletions
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 <linux/rmap.h>
#include <linux/mempolicy.h>
#include <linux/key.h>
-#include <linux/buffer_head.h>
#include <linux/page_ext.h>
#include <linux/debug_locks.h>
#include <linux/debugobjects.h>
@@ -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();

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