linux-kernel - RE: [PATCH 1/2] sched/wait: Break up long wake list walk

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Date:   Tue, 22 Aug 2017 19:55:37 +0000
From:   "Liang, Kan" <kan.liang@...el.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
CC:     Mel Gorman <mgorman@...hsingularity.net>,
        Mel Gorman <mgorman@...e.de>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Ingo Molnar" <mingo@...e.hu>, Andi Kleen <ak@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>,
        linux-mm <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/2] sched/wait: Break up long wake list walk

 
> So I propose testing the attached trivial patch. 

It doesn’t work. 
The call stack is the same.

   100.00%  (ffffffff821af140)
            |
            ---wait_on_page_bit
               __migration_entry_wait
               migration_entry_wait
               do_swap_page
               __handle_mm_fault
               handle_mm_fault
               __do_page_fault
               do_page_fault
               page_fault
               |
               |--40.62%--0x123a2
               |          start_thread
               |


> It may not do anything at all.
> But the existing code is actually doing extra work just to be fragile, in case the
> scenario above can happen.
> 
> Comments?
> 
>                 Linus