linux-kernel - Re: [PATCH v2 3/8] mm: Optimise madvise WILLNEED

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Message-ID: <20200914165032.GS6583@casper.infradead.org>
Date:   Mon, 14 Sep 2020 17:50:32 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Qian Cai <cai@...hat.com>
Cc:     linux-mm@...ck.org, intel-gfx@...ts.freedesktop.org,
        Huang Ying <ying.huang@...el.com>,
        Hugh Dickins <hughd@...gle.com>, linux-kernel@...r.kernel.org,
        Chris Wilson <chris@...is-wilson.co.uk>,
        William Kucharski <william.kucharski@...cle.com>,
        Johannes Weiner <hannes@...xchg.org>, cgroups@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Matthew Auld <matthew.auld@...el.com>
Subject: Re: [PATCH v2 3/8] mm: Optimise madvise WILLNEED

On Mon, Sep 14, 2020 at 12:17:07PM -0400, Qian Cai wrote:
> Reverting the "Return head pages from find_*_entry" patchset [1] up to this
> patch fixed the issue that LTP madvise06 test [2] would trigger endless soft-
> lockups below. It does not help after applied patches fixed other separate
> issues in the patchset [3][4].

Thanks for the report.  Could you try this?

diff --git a/mm/madvise.c b/mm/madvise.c
index 96189acd6969..2d9ceccb338d 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -234,6 +234,7 @@ static void force_shm_swapin_readahead(struct vm_area_struct *vma,
 
 		if (!xa_is_value(page))
 			continue;
+		xas_pause(&xas);
 		rcu_read_unlock();
 
 		swap = radix_to_swp_entry(page);
@@ -243,7 +244,6 @@ static void force_shm_swapin_readahead(struct vm_area_struct *vma,
 			put_page(page);
 
 		rcu_read_lock();
-		xas_reset(&xas);
 	}
 	rcu_read_unlock();