linux-kernel - Re: [RFC PATCH] mm/hugetlb: Avoid soft lockup in set_max_huge

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Message-ID: <5797916B.2020008@gmail.com>
Date:	Wed, 27 Jul 2016 00:35:55 +0800
From:	hejianet <hejianet@...il.com>
To:	Dave Hansen <dave.hansen@...ux.intel.com>, linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Mike Kravetz <mike.kravetz@...cle.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Michal Hocko <mhocko@...e.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [RFC PATCH] mm/hugetlb: Avoid soft lockup in set_max_huge_pages()



On 7/26/16 11:58 PM, Dave Hansen wrote:
> On 07/26/2016 08:44 AM, Jia He wrote:
>> This patch is to fix such soft lockup. I thouhgt it is safe to call
>> cond_resched() because alloc_fresh_gigantic_page and alloc_fresh_huge_page
>> are out of spin_lock/unlock section.
> Yikes.  So the call site for both the things you patch is this:
>
>>          while (count > persistent_huge_pages(h)) {
> ...
>>                  spin_unlock(&hugetlb_lock);
>>                  if (hstate_is_gigantic(h))
>>                          ret = alloc_fresh_gigantic_page(h, nodes_allowed);
>>                  else
>>                          ret = alloc_fresh_huge_page(h, nodes_allowed);
>>                  spin_lock(&hugetlb_lock);
> and you choose to patch both of the alloc_*() functions.  Why not just
> fix it at the common call site?  Seems like that
> spin_lock(&hugetlb_lock) could be a cond_resched_lock() which would fix
> both cases.
>
> Also, putting that cond_resched() inside the for_each_node*() loop is an
> odd choice.  It seems to indicate that the loops can take a long time,
> which really isn't the case.  The _loop_ isn't long, right?
Yes,thanks for the suggestions
Will send out V2 later

B.R.