On Fri, Sep 29, 2017 at 4:51 PM, huang ying
<huang.ying.caritas@xxxxxxxxx> wrote:
> On Wed, Sep 20, 2017 at 1:43 PM, Minchan Kim <minchan@xxxxxxxxxx> wrote:
[snip]
>> diff --git a/mm/memory.c b/mm/memory.c
>> index ec4e15494901..163ab2062385 100644
>> --- a/mm/memory.c
>> +++ b/mm/memory.c
>> @@ -2842,7 +2842,7 @@ EXPORT_SYMBOL(unmap_mapping_range);
>> int do_swap_page(struct vm_fault *vmf)
>> {
>> struct vm_area_struct *vma = vmf->vma;
>> - struct page *page = NULL, *swapcache;
>> + struct page *page = NULL, *swapcache = NULL;
>> struct mem_cgroup *memcg;
>> struct vma_swap_readahead swap_ra;
>> swp_entry_t entry;
>> @@ -2881,17 +2881,35 @@ int do_swap_page(struct vm_fault *vmf)
>> }
>> goto out;
>> }
>> +
>> +
>> delayacct_set_flag(DELAYACCT_PF_SWAPIN);
>> if (!page)
>> page = lookup_swap_cache(entry, vma_readahead ? vma : NULL,
>> vmf->address);
>> if (!page) {
>> - if (vma_readahead)
>> - page = do_swap_page_readahead(entry,
>> - GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
>> - else
>> - page = swapin_readahead(entry,
>> - GFP_HIGHUSER_MOVABLE, vma, vmf->address);
>> + struct swap_info_struct *si = swp_swap_info(entry);
>> +
>> + if (!(si->flags & SWP_SYNCHRONOUS_IO)) {
>> + if (vma_readahead)
>> + page = do_swap_page_readahead(entry,
>> + GFP_HIGHUSER_MOVABLE, vmf, &swap_ra);
>> + else
>> + page = swapin_readahead(entry,
>> + GFP_HIGHUSER_MOVABLE, vma, vmf->address);
>> + swapcache = page;
>> + } else {
>> + /* skip swapcache */
>> + page = alloc_page_vma(GFP_HIGHUSER_MOVABLE, vma, vmf->address);
>> + if (page) {
>> + __SetPageLocked(page);
>> + __SetPageSwapBacked(page);
>> + set_page_private(page, entry.val);
>> + lru_cache_add_anon(page);
>> + swap_readpage(page, true);
>> + }
>> + }
>
> I have a question for this. If a page is mapped in multiple processes
> (for example, because of fork). With swap cache, after swapping out
> and swapping in, the page will be still shared by these processes.
> But with your changes, it appears that there will be multiple pages
> with same contents mapped in multiple processes, even if the page
> isn't written in these processes. So this may waste some memory in
> some situation? And copying from device is even faster than looking
> up swap cache in your system?
Hi, Minchan,
Could you help me on this?
Best Regards,
Huang, Ying
[snip]
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