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SubjectRe: [PATCH -mm] mm, swap: Fix false error message in __swp_swapcount()
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Michal Hocko <mhocko@kernel.org> writes:

> On Tue 24-10-17 23:15:32, Huang, Ying wrote:
>> Hi, Michal,
>>
>> Michal Hocko <mhocko@kernel.org> writes:
>>
>> > On Tue 24-10-17 10:47:00, Huang, Ying wrote:
>> >> From: Ying Huang <ying.huang@intel.com>
>> >>
>> >> __swp_swapcount() is used in __read_swap_cache_async(). Where the
>> >> invalid swap entry (offset > max) may be supplied during swap
>> >> readahead. But __swp_swapcount() will print error message for these
>> >> expected invalid swap entry as below, which will make the users
>> >> confusing.
>> > ^^
>> > confused... And I have to admit this changelog has left me confused as
>> > well. What is an invalid swap entry in the readahead? Ohh, let me
>> > re-real Fixes: commit. It didn't really help "We can avoid needlessly
>> > allocating page for swap slots that are not used by anyone. No pages
>> > have to be read in for these slots."
>> >
>> > Could you be more specific about when and how this happens please?
>>
>> Sorry for confusing.
>>
>> When page fault occurs for a swap entry, the original swap readahead
>> (not new VMA base swap readahead) may readahead several swap entries
>> after the fault swap entry. The readahead algorithm calculates some of
>> the swap entries to readahead via increasing the offset of the fault
>> swap entry without checking whether they are beyond the end of the swap
>> device and it rely on the __swp_swapcount() and swapcache_prepare() to
>> check it. Although __swp_swapcount() checks for the swap entry passed
>> in, it will complain with error message for the expected invalid swap
>> entry. This makes the end user confusing.
>>
>> Is this a little clearer.
>
> yes, this makes more sense (modulo the same typo ;)). Can you make this
> information into the changelog please? Thanks.

Oh, Yes! I should fix it. Sure, I will add this into the changelog.

Best Regards,
Huang, Ying

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