Re: [patch 21/21] cull non-reclaimable anon pages from the LRU at fault time

[Lee Schermerhorn <Lee.Schermerhorn@hp.com>]

On Thu, 2008-02-28 at 14:29 -0500, Rik van Riel wrote:

corrections to description in case we decide to keep this patch.


> V2 -> V3:
> + rebase to 23-mm1 atop RvR's split lru series.
> 
> V1 -> V2:
> +  no changes
> 
> Optional part of "noreclaim infrastructure"
> 
> In the fault paths that install new anonymous pages, check whether
> the page is reclaimable or not using lru_cache_add_active_or_noreclaim().
> If the page is reclaimable, just add it to the active lru list [via
> the pagevec cache], else add it to the noreclaim list.  
> 
> This "proactive" culling in the fault path mimics the handling of
> mlocked pages in Nick Piggin's series to keep mlocked pages off
> the lru lists.
> 
> Notes:
> 
> 1) This patch is optional--e.g., if one is concerned about the
>    additional test in the fault path.  We can defer the moving of
>    nonreclaimable pages until when vmscan [shrink_*_list()]
>    encounters them.  Vmscan will only need to handle such pages
>    once.
> 
> 2) I moved the call to page_add_new_anon_rmap() to before the test
>    for page_reclaimable() and thus before the calls to
>    lru_cache_add_{active|noreclaim}(), so that page_reclaimable()
>    could recognize the page as anon, 
<snip the bit about the vma arg.  replaced with new note 3 below>
>    TBD:   I think this reordering is OK, but the previous order may
>    have existed to close some obscure race?
> 
<delete prev note 3, as it referred to patches that are no longer in the
series [altho' I continue to maintain them separately, "just in case"].
replace with this note about vma arg to page_reclaimable()>

3) The 'vma' argument to page_reclaimable() is require to notice that
   we're faulting a page into an mlock()ed vma w/o having to scan the
   page's rmap in the fault path.   Culling mlock()ed anon pages is
   currently the only reason for this patch.
> 
> Signed-off-by:  Lee Schermerhorn <lee.schermerhorn@hp.com>
> Signed-off-by:  Rik van Riel <riel@redhat.com>
> 
> Index: linux-2.6.25-rc2-mm1/mm/memory.c
> ===================================================================
> --- linux-2.6.25-rc2-mm1.orig/mm/memory.c	2008-02-28 00:27:06.000000000 -0500
> +++ linux-2.6.25-rc2-mm1/mm/memory.c	2008-02-28 12:49:23.000000000 -0500
> @@ -1678,7 +1678,7 @@ gotten:
>  		set_pte_at(mm, address, page_table, entry);
>  		update_mmu_cache(vma, address, entry);
>  		SetPageSwapBacked(new_page);
> -		lru_cache_add_active_anon(new_page);
> +		lru_cache_add_active_or_noreclaim(new_page, vma);
>  		page_add_new_anon_rmap(new_page, vma, address);
>  
>  		/* Free the old page.. */
> @@ -2150,7 +2150,7 @@ static int do_anonymous_page(struct mm_s
>  		goto release;
>  	inc_mm_counter(mm, anon_rss);
>  	SetPageSwapBacked(page);
> -	lru_cache_add_active_anon(page);
> +	lru_cache_add_active_or_noreclaim(page, vma);
>  	page_add_new_anon_rmap(page, vma, address);
>  	set_pte_at(mm, address, page_table, entry);
>  
> @@ -2292,10 +2292,10 @@ static int __do_fault(struct mm_struct *
>  			entry = maybe_mkwrite(pte_mkdirty(entry), vma);
>  		set_pte_at(mm, address, page_table, entry);
>  		if (anon) {
> -                        inc_mm_counter(mm, anon_rss);
> +			inc_mm_counter(mm, anon_rss);
>  			SetPageSwapBacked(page);
> -                        lru_cache_add_active_anon(page);
> -                        page_add_new_anon_rmap(page, vma, address);
> +			lru_cache_add_active_or_noreclaim(page, vma);
> +			page_add_new_anon_rmap(page, vma, address);
>  		} else {
>  			inc_mm_counter(mm, file_rss);
>  			page_add_file_rmap(page);
> Index: linux-2.6.25-rc2-mm1/mm/swap_state.c
> ===================================================================
> --- linux-2.6.25-rc2-mm1.orig/mm/swap_state.c	2008-02-28 00:29:51.000000000 -0500
> +++ linux-2.6.25-rc2-mm1/mm/swap_state.c	2008-02-28 12:49:23.000000000 -0500
> @@ -300,7 +300,10 @@ struct page *read_swap_cache_async(swp_e
>  			/*
>  			 * Initiate read into locked page and return.
>  			 */
> -			lru_cache_add_anon(new_page);
> +			if (!page_reclaimable(new_page, vma))
> +				lru_cache_add_noreclaim(new_page);
> +			else
> +				lru_cache_add_anon(new_page);
>  			swap_readpage(NULL, new_page);
>  			return new_page;
>  		}
>