lkml.org 
[lkml]   [2017]   [Oct]   [8]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v2 4/4] mm:swap: skip swapcache for swapin of synchronous device
On Fri, Sep 29, 2017 at 4:51 PM, huang ying
<huang.ying.caritas@gmail.com> wrote:
> On Wed, Sep 20, 2017 at 1:43 PM, Minchan Kim <minchan@kernel.org> 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]

\
 
 \ /
  Last update: 2017-10-09 03:26    [W:0.111 / U:0.456 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site