Evicting Anonymous pages.

[Prateek Sharma]

On Tue, Sep 27, 2011 at 11:42 PM, Mulyadi Santosa
<mulyadi.santosa at gmail.com> wrote:
> Hi :)
>
> On Wed, Sep 28, 2011 at 00:14, Prateek Sharma <prateek3.14 at gmail.com> wrote:
>> Hello everyone,
>>  I am trying to understand the kernel page frame reclaiming
>> mechanism, but one thing's bothering me:
>> How does the kernel 'know' which anonymous pages to evict? In the LRU
>> scheme,  'referenced/used' information for each page is required
>> (AFAIK). But anonymous pages can be used by user processes 'at any
>> time' without the kernel knowing about it.
>
> Same question hog my mind too so far :)
>
> The only satisfying self answer I could deduce is:
> kernel can't track every access to pages when you do it like e.g mov
> %ax,8(%esp). What kernel could track is when you access data via
> wrappers. I forgot which ones, but remember some of them are updating
> those "referenced" etc flags. Perhaps something like get_pages or
> alike.
>
> --
> regards,
>
> Mulyadi Santosa
> Freelance Linux trainer and consultant
>

page_referenced_anon is called for anonymous pages by page_referenced.
And as far as i could figure out, that uses mmu_notifiers. [calls
pmdp_clear_flush_young_notify]

Whether every anonymous page access is trapped, or only a few of them,
i have not yet figured out.

Linux-mm seems to be full of magic!