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SubjectRe: [PATCH -mm -v10 1/3] mm, THP, swap: Delay splitting THP during swap out
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Minchan Kim <minchan@kernel.org> writes:

> On Wed, May 10, 2017 at 09:56:54AM -0400, Johannes Weiner wrote:
>> Hi Michan,
>>
>> On Tue, May 02, 2017 at 08:53:32AM +0900, Minchan Kim wrote:
>> > @@ -1144,7 +1144,7 @@ void swap_free(swp_entry_t entry)
>> > /*
>> > * Called after dropping swapcache to decrease refcnt to swap entries.
>> > */
>> > -void swapcache_free(swp_entry_t entry)
>> > +void __swapcache_free(swp_entry_t entry)
>> > {
>> > struct swap_info_struct *p;
>> >
>> > @@ -1156,7 +1156,7 @@ void swapcache_free(swp_entry_t entry)
>> > }
>> >
>> > #ifdef CONFIG_THP_SWAP
>> > -void swapcache_free_cluster(swp_entry_t entry)
>> > +void __swapcache_free_cluster(swp_entry_t entry)
>> > {
>> > unsigned long offset = swp_offset(entry);
>> > unsigned long idx = offset / SWAPFILE_CLUSTER;
>> > @@ -1182,6 +1182,14 @@ void swapcache_free_cluster(swp_entry_t entry)
>> > }
>> > #endif /* CONFIG_THP_SWAP */
>> >
>> > +void swapcache_free(struct page *page, swp_entry_t entry)
>> > +{
>> > + if (!PageTransHuge(page))
>> > + __swapcache_free(entry);
>> > + else
>> > + __swapcache_free_cluster(entry);
>> > +}
>>
>> I don't think this is cleaner :/
>>
>> On your second patch:
>>
>> > @@ -1125,8 +1125,28 @@ static unsigned long shrink_page_list(struct list_head *page_list,
>> > !PageSwapCache(page)) {
>> > if (!(sc->gfp_mask & __GFP_IO))
>> > goto keep_locked;
>> > - if (!add_to_swap(page, page_list))
>> > +swap_retry:
>> > + /*
>> > + * Retry after split if we fail to allocate
>> > + * swap space of a THP.
>> > + */
>> > + if (!add_to_swap(page)) {
>> > + if (!PageTransHuge(page) ||
>> > + split_huge_page_to_list(page, page_list))
>> > + goto activate_locked;
>> > + goto swap_retry;
>> > + }
>>
>> This is definitely better.
>
> Thanks.
>
>>
>> However, I think it'd be cleaner without the label here:
>>
>> if (!add_to_swap(page)) {
>> if (!PageTransHuge(page))
>> goto activate_locked;
>> /* Split THP and swap individual base pages */
>> if (split_huge_page_to_list(page, page_list))
>> goto activate_locked;
>> if (!add_to_swap(page))
>> goto activate_locked;
>
> Yes.
>
>> }
>>
>> > + /*
>> > + * Got swap space successfully. But unfortunately,
>> > + * we don't support a THP page writeout so split it.
>> > + */
>> > + if (PageTransHuge(page) &&
>> > + split_huge_page_to_list(page, page_list)) {
>> > + delete_from_swap_cache(page);
>> > goto activate_locked;
>> > + }
>>
>> Pulling this out of add_to_swap() is an improvement for sure. Add an
>> XXX: before that "we don't support THP writes" comment for good
>> measure :)
>
> Sure.
>
> It could be a separate patch which makes add_to_swap clean via
> removing page_list argument but I hope Huang take/fold it when he
> resend it because it would be more important with THP swap.

Sure. I will take this patch as one patch of the THP swap series.
Because the first patch of the THP swap series is a little big, I don't
think it is a good idea to fold this patch into it. Could you update
the patch according to Johannes' comments and resend it?

Best Regards,
Huang, Ying

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