Messages in this thread | | | Subject | Re: [PATCHv2 4/8] khugepaged: Drain LRU add pagevec after swapin | From | Yang Shi <> | Date | Wed, 8 Apr 2020 11:42:55 -0700 |
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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 <kirill.shutemov@linux.intel.com> >>> --- >>> 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.
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