From: Joerg Roedel <joro@8bytes.org>
To: Alex Shi <alex.shi@linux.alibaba.com>,
Robin Murphy <robin.murphy@arm.com>
Cc: "Mika Penttilä" <mika.penttila@nextfour.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>,
"Matthew Wilcox" <willy@infradead.org>,
"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>,
iommu@lists.linux-foundation.org
Subject: Re: a question of split_huge_page
Date: Fri, 10 Jul 2020 14:56:23 +0200 [thread overview]
Message-ID: <20200710125623.GH27672@8bytes.org> (raw)
In-Reply-To: <50113530-fae5-bb36-56c2-5b5c4f90426d@linux.alibaba.com>
Adding Robin.
On Fri, Jul 10, 2020 at 05:34:52PM +0800, Alex Shi wrote:
> 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 12:56 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
2020-07-10 12:56 ` Joerg Roedel [this message]
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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