Re: [patch 13/13] mm: memcontrol: rewrite uncharge API

[Miklos Szeredi]

On Fri, Jul 18, 2014 at 4:45 PM, Johannes Weiner <hannes@xxxxxxxxxxx> wrote:

> I assumed the source page would always be new, according to this part
> in fuse_try_move_page():
>
>         /*
>          * This is a new and locked page, it shouldn't be mapped or
>          * have any special flags on it
>          */
>         if (WARN_ON(page_mapped(oldpage)))
>                 goto out_fallback_unlock;
>         if (WARN_ON(page_has_private(oldpage)))
>                 goto out_fallback_unlock;
>         if (WARN_ON(PageDirty(oldpage) || PageWriteback(oldpage)))
>                 goto out_fallback_unlock;
>         if (WARN_ON(PageMlocked(oldpage)))
>                 goto out_fallback_unlock;
>
> However, it's in the page cache and I can't really convince myself
> that it's not also on the LRU.  Miklos, I have trouble pinpointing
> where oldpage is instantiated exactly and what state it might be in -
> can it already be on the LRU?

oldpage comes from ->readpages() (*NOT* ->readpage()), i.e. readahead.

AFAICS it is added to the LRU in read_cache_pages(), so it looks like
it is definitely on the LRU at that point.

Thanks,
Miklos
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