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Date:   Mon, 2 Nov 2020 10:18:07 -0500
From:   Johannes Weiner <hannes@cmpxchg.org>
To:     Alex Shi <alex.shi@linux.alibaba.com>
Cc:     akpm@linux-foundation.org, mgorman@techsingularity.net,
        tj@kernel.org, hughd@google.com, khlebnikov@yandex-team.ru,
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        cgroups@vger.kernel.org, shakeelb@google.com,
        iamjoonsoo.kim@lge.com, richard.weiyang@gmail.com,
        kirill@shutemov.name, alexander.duyck@gmail.com,
        rong.a.chen@intel.com, mhocko@suse.com, vdavydov.dev@gmail.com,
        shy828301@gmail.com
Subject: Re: [PATCH v20 16/20] mm/compaction: do page isolation first in
 compaction
Message-ID: <20201102151807.GI724984@cmpxchg.org>
References: <1603968305-8026-1-git-send-email-alex.shi@linux.alibaba.com>
 <1603968305-8026-17-git-send-email-alex.shi@linux.alibaba.com>
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On Thu, Oct 29, 2020 at 06:45:01PM +0800, Alex Shi wrote:
> Currently, compaction would get the lru_lock and then do page isolation
> which works fine with pgdat->lru_lock, since any page isoltion would
> compete for the lru_lock. If we want to change to memcg lru_lock, we
> have to isolate the page before getting lru_lock, thus isoltion would
> block page's memcg change which relay on page isoltion too. Then we
> could safely use per memcg lru_lock later.
> 
> The new page isolation use previous introduced TestClearPageLRU() +
> pgdat lru locking which will be changed to memcg lru lock later.
> 
> Hugh Dickins <hughd@google.com> fixed following bugs in this patch's
> early version:
> 
> Fix lots of crashes under compaction load: isolate_migratepages_block()
> must clean up appropriately when rejecting a page, setting PageLRU again
> if it had been cleared; and a put_page() after get_page_unless_zero()
> cannot safely be done while holding locked_lruvec - it may turn out to
> be the final put_page(), which will take an lruvec lock when PageLRU.
> And move __isolate_lru_page_prepare back after get_page_unless_zero to
> make trylock_page() safe:
> trylock_page() is not safe to use at this time: its setting PG_locked
> can race with the page being freed or allocated ("Bad page"), and can
> also erase flags being set by one of those "sole owners" of a freshly
> allocated page who use non-atomic __SetPageFlag().
> 
> Suggested-by: Johannes Weiner <hannes@cmpxchg.org>
> Signed-off-by: Alex Shi <alex.shi@linux.alibaba.com>
> Acked-by: Hugh Dickins <hughd@google.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: linux-kernel@vger.kernel.org
> Cc: linux-mm@kvack.org

Acked-by: Johannes Weiner <hannes@cmpxchg.org>