From: Alex Shi <alex.shi@linux.alibaba.com>
To: "Mika Penttilä" <mika.penttila@nextfour.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
"Matthew Wilcox" <willy@infradead.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>,
Linux-MM <linux-mm@kvack.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Hugh Dickins <hughd@google.com>, Joerg Roedel <joro@8bytes.org>,
iommu@lists.linux-foundation.org
Subject: Re: a question of split_huge_page
Date: Fri, 10 Jul 2020 17:34:52 +0800 [thread overview]
Message-ID: <50113530-fae5-bb36-56c2-5b5c4f90426d@linux.alibaba.com> (raw)
In-Reply-To: <441ebbeb-0408-e22e-20f4-1be571c4a18e@nextfour.com>
在 2020/7/10 下午1:28, Mika Penttilä 写道:
>
>
> On 10.7.2020 7.51, Alex Shi wrote:
>>
>> 在 2020/7/10 上午12:07, Kirill A. Shutemov 写道:
>>> On Thu, Jul 09, 2020 at 04:50:02PM +0100, Matthew Wilcox wrote:
>>>> On Thu, Jul 09, 2020 at 11:11:11PM +0800, Alex Shi wrote:
>>>>> Hi Kirill & Matthew,
>>>>>
>>>>> In the func call chain, from split_huge_page() to lru_add_page_tail(),
>>>>> Seems tail pages are added to lru list at line 963, but in this scenario
>>>>> the head page has no lru bit and isn't set the bit later. Why we do this?
>>>>> or do I miss sth?
>>>> I don't understand how we get to split_huge_page() with a page that's
>>>> not on an LRU list. Both anonymous and page cache pages should be on
>>>> an LRU list. What am I missing?>
>>
>> Thanks a lot for quick reply!
>> What I am confusing is the call chain: __iommu_dma_alloc_pages()
>> to split_huge_page(), in the func, splited page,
>> page = alloc_pages_node(nid, alloc_flags, order);
>> And if the pages were added into lru, they maybe reclaimed and lost,
>> that would be a panic bug. But in fact, this never happened for long time.
>> Also I put a BUG() at the line, it's nevre triggered in ltp, and run_vmtests
>
>
> In __iommu_dma_alloc_pages, after split_huge_page(), who is taking a
> reference on tail pages? Seems tail pages are freed and the function
> errornously returns them in pages[] array for use?
>
CC Joerg and iommu list,
That's a good question. seems the split_huge_page was never triggered here,
since the func would check the PageLock first. and have page->mapping and PageAnon
check, any of them couldn't be matched for the alloced page.
Hi Joerg,
would you like look into this? do we still need the split_huge_page() here?
Thanks
Alex
int split_huge_page_to_list(struct page *page, struct list_head *list)
{
struct page *head = compound_head(page);
struct deferred_split *ds_queue = get_deferred_split_queue(head);
struct anon_vma *anon_vma = NULL;
struct address_space *mapping = NULL;
int count, mapcount, extra_pins, ret;
pgoff_t end;
VM_BUG_ON_PAGE(is_huge_zero_page(head), head);
VM_BUG_ON_PAGE(!PageLocked(head), head); <==
>
next prev parent reply other threads:[~2020-07-10 9:35 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-09 15:11 a question of split_huge_page Alex Shi
2020-07-09 15:50 ` Matthew Wilcox
2020-07-09 16:07 ` Kirill A. Shutemov
2020-07-10 4:51 ` Alex Shi
2020-07-10 5:28 ` Mika Penttilä
2020-07-10 7:00 ` Alex Shi
2020-07-10 7:22 ` Mika Penttilä
2020-07-10 9:34 ` Alex Shi [this message]
2020-07-10 12:56 ` Joerg Roedel
2020-07-10 17:29 ` Yang Shi
2020-07-10 10:33 ` Kirill A. Shutemov
2020-07-10 14:23 ` Alex Shi
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