__collapse_huge_page_isolate() may fail due to extra pin in the LRU add
pagevec. It's petty common for swapin case: we swap in pages just to
fail due to the extra pin.
Drain LRU add pagevec on sucessfull swapin.
Signed-off-by: Kirill A. Shutemov <[email protected]>
---
mm/khugepaged.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index fdc10ffde1ca..57ff287caf6b 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -940,6 +940,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
}
vmf.pte--;
pte_unmap(vmf.pte);
+
+ /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
+ if (swapped_in)
+ lru_add_drain();
+
trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
return true;
}
--
2.26.0
On 3 Apr 2020, at 7:29, Kirill A. Shutemov wrote:
> External email: Use caution opening links or attachments
>
>
> __collapse_huge_page_isolate() may fail due to extra pin in the LRU add
> pagevec. It's petty common for swapin case: we swap in pages just to
s/petty/pretty
> fail due to the extra pin.
>
> Drain LRU add pagevec on sucessfull swapin.
s/sucessfull/successful
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> ---
> mm/khugepaged.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index fdc10ffde1ca..57ff287caf6b 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -940,6 +940,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
> }
> vmf.pte--;
> pte_unmap(vmf.pte);
> +
> + /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
> + if (swapped_in)
> + lru_add_drain();
> +
> trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
> return true;
> }
> --
> 2.26.0
—
Best Regards,
Yan Zi
On 4/3/20 4:29 AM, Kirill A. Shutemov wrote:
> __collapse_huge_page_isolate() may fail due to extra pin in the LRU add
> pagevec. It's petty common for swapin case: we swap in pages just to
> fail due to the extra pin.
>
> Drain LRU add pagevec on sucessfull swapin.
>
> Signed-off-by: Kirill A. Shutemov <[email protected]>
> ---
> mm/khugepaged.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index fdc10ffde1ca..57ff287caf6b 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -940,6 +940,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
> }
> vmf.pte--;
> pte_unmap(vmf.pte);
> +
> + /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
> + if (swapped_in)
> + lru_add_drain();
There is already lru_add_drain() called in swap readahead path, please
see swap_vma_readahead() and swap_cluster_readahead().
The extra call to draining lru seems unnecessary.
> +
> trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 1);
> return true;
> }
On Mon, Apr 06, 2020 at 11:29:11AM -0700, Yang Shi wrote:
>
>
> On 4/3/20 4:29 AM, Kirill A. Shutemov wrote:
> > __collapse_huge_page_isolate() may fail due to extra pin in the LRU add
> > pagevec. It's petty common for swapin case: we swap in pages just to
> > fail due to the extra pin.
> >
> > Drain LRU add pagevec on sucessfull swapin.
> >
> > Signed-off-by: Kirill A. Shutemov <[email protected]>
> > ---
> > mm/khugepaged.c | 5 +++++
> > 1 file changed, 5 insertions(+)
> >
> > diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> > index fdc10ffde1ca..57ff287caf6b 100644
> > --- a/mm/khugepaged.c
> > +++ b/mm/khugepaged.c
> > @@ -940,6 +940,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
> > }
> > vmf.pte--;
> > pte_unmap(vmf.pte);
> > +
> > + /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
> > + if (swapped_in)
> > + lru_add_drain();
>
> There is already lru_add_drain() called in swap readahead path, please see
> swap_vma_readahead() and swap_cluster_readahead().
But not for synchronous case. See SWP_SYNCHRONOUS_IO branch in
do_swap_page().
Maybe we should drain it in swap_readpage() or in do_swap_page() after
swap_readpage()? I donno.
--
Kirill A. Shutemov
On 4/8/20 6:05 AM, Kirill A. Shutemov wrote:
> On Mon, Apr 06, 2020 at 11:29:11AM -0700, Yang Shi wrote:
>>
>> On 4/3/20 4:29 AM, Kirill A. Shutemov wrote:
>>> __collapse_huge_page_isolate() may fail due to extra pin in the LRU add
>>> pagevec. It's petty common for swapin case: we swap in pages just to
>>> fail due to the extra pin.
>>>
>>> Drain LRU add pagevec on sucessfull swapin.
>>>
>>> Signed-off-by: Kirill A. Shutemov <[email protected]>
>>> ---
>>> mm/khugepaged.c | 5 +++++
>>> 1 file changed, 5 insertions(+)
>>>
>>> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
>>> index fdc10ffde1ca..57ff287caf6b 100644
>>> --- a/mm/khugepaged.c
>>> +++ b/mm/khugepaged.c
>>> @@ -940,6 +940,11 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
>>> }
>>> vmf.pte--;
>>> pte_unmap(vmf.pte);
>>> +
>>> + /* Drain LRU add pagevec to remove extra pin on the swapped in pages */
>>> + if (swapped_in)
>>> + lru_add_drain();
>> There is already lru_add_drain() called in swap readahead path, please see
>> swap_vma_readahead() and swap_cluster_readahead().
> But not for synchronous case. See SWP_SYNCHRONOUS_IO branch in
> do_swap_page().
Aha, yes. I missed the synchronous case.
>
> Maybe we should drain it in swap_readpage() or in do_swap_page() after
> swap_readpage()? I donno.
It may be better to keep it as is. Draining lru for every page for
synchronous case in do_swap_page() path sounds not very productive.
Doing it in khugepaged seems acceptable. We just drain lru cache again
for non-synchronous case, but the cache may be already empty so it
should take very short time since nothing to drain.
>