Matthew Wilcox <wi...@infradead.org> writes:
> On Tue, Jul 23, 2019 at 01:08:42PM +0800, Huang, Ying wrote:
>> @@ -2489,6 +2491,14 @@ static void __split_huge_page(struct page *page,
>> struct list_head *list,
>> /* complete memcg works before add pages to LRU */
>> mem_cgroup_split_huge_fixup(head);
>>
>> + if (PageAnon(head) && PageSwapCache(head)) {
>> + swp_entry_t entry = { .val = page_private(head) };
>> +
>> + offset = swp_offset(entry);
>> + swap_cache = swap_address_space(entry);
>> + xa_lock(&swap_cache->i_pages);
>> + }
>> +
>> for (i = HPAGE_PMD_NR - 1; i >= 1; i--) {
>> __split_huge_page_tail(head, i, lruvec, list);
>> /* Some pages can be beyond i_size: drop them from page cache */
>> @@ -2501,6 +2511,9 @@ static void __split_huge_page(struct page *page,
>> struct list_head *list,
>> } else if (!PageAnon(page)) {
>> __xa_store(&head->mapping->i_pages, head[i].index,
>> head + i, 0);
>> + } else if (swap_cache) {
>> + __xa_store(&swap_cache->i_pages, offset + i,
>> + head + i, 0);
>
> I tried something along these lines (though I think I messed up the offset
> calculation which is why it wasn't working for me). My other concern
> was with the case where SWAPFILE_CLUSTER was less than HPAGE_PMD_NR.
> Don't we need to drop the lock and look up a new swap_cache if offset >=
> SWAPFILE_CLUSTER?
In swapfile.c, there is
#ifdef CONFIG_THP_SWAP
#define SWAPFILE_CLUSTER HPAGE_PMD_NR
...
#else
#define SWAPFILE_CLUSTER 256
...
#endif
So, if a THP is in swap cache, then SWAPFILE_CLUSTER equals
HPAGE_PMD_NR.
And there is one swap address space for each 64M swap space. So one THP
will be in one swap address space.
In swap.h, there is
/* One swap address space for each 64M swap space */
#define SWAP_ADDRESS_SPACE_SHIFT 14
#define SWAP_ADDRESS_SPACE_PAGES (1 << SWAP_ADDRESS_SPACE_SHIFT)
Best Regards,
Huang, Ying
