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SubjectRe: [PATCH v4] page cache: Store only head pages in i_pages
Date
Quoting Matthew Wilcox (2019-03-07 15:30:51)
> Transparent Huge Pages are currently stored in i_pages as pointers to
> consecutive subpages. This patch changes that to storing consecutive
> pointers to the head page in preparation for storing huge pages more
> efficiently in i_pages.
>
> Large parts of this are "inspired" by Kirill's patch
> https://lore.kernel.org/lkml/20170126115819.58875-2-kirill.shutemov@linux.intel.com/
>
> Signed-off-by: Matthew Wilcox <willy@infradead.org>
> Acked-by: Jan Kara <jack@suse.cz>
> Reviewed-by: Kirill Shutemov <kirill@shutemov.name>
> Reviewed-and-tested-by: Song Liu <songliubraving@fb.com>
> Tested-by: William Kucharski <william.kucharski@oracle.com>
> Reviewed-by: William Kucharski <william.kucharski@oracle.com>

I've bisected some new softlockups under THP mempressure to this patch.
They are all rcu stalls that look similar to:
[ 242.645276] rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
[ 242.645293] rcu: Tasks blocked on level-0 rcu_node (CPUs 0-3): P828
[ 242.645301] (detected by 1, t=5252 jiffies, g=55501, q=221)
[ 242.645307] gem_syslatency R running task 0 828 815 0x00004000
[ 242.645315] Call Trace:
[ 242.645326] ? __schedule+0x1a0/0x440
[ 242.645332] ? preempt_schedule_irq+0x27/0x50
[ 242.645337] ? apic_timer_interrupt+0xa/0x20
[ 242.645342] ? xas_load+0x3c/0x80
[ 242.645347] ? xas_load+0x8/0x80
[ 242.645353] ? find_get_entry+0x4f/0x130
[ 242.645358] ? pagecache_get_page+0x2b/0x210
[ 242.645364] ? lookup_swap_cache+0x42/0x100
[ 242.645371] ? do_swap_page+0x6f/0x600
[ 242.645375] ? unmap_region+0xc2/0xe0
[ 242.645380] ? __handle_mm_fault+0x7a9/0xfa0
[ 242.645385] ? handle_mm_fault+0xc2/0x1c0
[ 242.645393] ? __do_page_fault+0x198/0x410
[ 242.645399] ? page_fault+0x5/0x20
[ 242.645404] ? page_fault+0x1b/0x20

Any suggestions as to what information you might want?
-Chris

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