linux-kernel - Re: [PATCH v3 5/5] Documentation/mm: Update references to __m[un]lock_page() to *

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Message-ID: <ef422b84-cd33-69c7-9fef-cc8d1d45651c@suse.cz>
Date:   Thu, 12 Jan 2023 12:04:53 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Lorenzo Stoakes <lstoakes@...il.com>, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-kernel@...r.kernel.org
Cc:     Matthew Wilcox <willy@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        Liam Howlett <liam.howlett@...cle.com>,
        William Kucharski <william.kucharski@...cle.com>,
        Christian Brauner <brauner@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Mike Rapoport <rppt@...nel.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH v3 5/5] Documentation/mm: Update references to
 __m[un]lock_page() to *_folio()

On 12/26/22 09:44, Lorenzo Stoakes wrote:
> We now pass folios to these functions, so update the documentation
> accordingly.
> 
> Additionally, correct the outdated reference to __pagevec_lru_add_fn(), the
> referenced action occurs in __munlock_folio() directly now.
> 
> Signed-off-by: Lorenzo Stoakes <lstoakes@...il.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

With:

> ---
>  Documentation/mm/unevictable-lru.rst | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/Documentation/mm/unevictable-lru.rst b/Documentation/mm/unevictable-lru.rst
> index 4a0e158aa9ce..153629e0c100 100644
> --- a/Documentation/mm/unevictable-lru.rst
> +++ b/Documentation/mm/unevictable-lru.rst
> @@ -308,22 +308,22 @@ do end up getting faulted into this VM_LOCKED VMA, they will be handled in the
>  fault path - which is also how mlock2()'s MLOCK_ONFAULT areas are handled.
>  
>  For each PTE (or PMD) being faulted into a VMA, the page add rmap function
> -calls mlock_vma_page(), which calls mlock_page() when the VMA is VM_LOCKED
> +calls mlock_vma_page(), which calls mlock_folio() when the VMA is VM_LOCKED
>  (unless it is a PTE mapping of a part of a transparent huge page).  Or when
>  it is a newly allocated anonymous page, lru_cache_add_inactive_or_unevictable()

Think it would be more appropriate now:    ^ folio_add_lru_vma()

> -calls mlock_new_page() instead: similar to mlock_page(), but can make better
> +calls mlock_new_folio() instead: similar to mlock_folio(), but can make better
>  judgments, since this page is held exclusively and known not to be on LRU yet.
>  
> -mlock_page() sets PageMlocked immediately, then places the page on the CPU's

		     PG_mlocked?

> -mlock pagevec, to batch up the rest of the work to be done under lru_lock by
> -__mlock_page().  __mlock_page() sets PageUnevictable, initializes mlock_count

					PG_unevictable

ditto below

> +mlock_folio() sets PageMlocked immediately, then places the page on the CPU's
> +mlock folio batch, to batch up the rest of the work to be done under lru_lock by
> +__mlock_folio().  __mlock_folio() sets PageUnevictable, initializes mlock_count
>  and moves the page to unevictable state ("the unevictable LRU", but with
>  mlock_count in place of LRU threading).  Or if the page was already PageLRU
>  and PageUnevictable and PageMlocked, it simply increments the mlock_count.
>  
>  But in practice that may not work ideally: the page may not yet be on an LRU, or
>  it may have been temporarily isolated from LRU.  In such cases the mlock_count
> -field cannot be touched, but will be set to 0 later when __pagevec_lru_add_fn()
> +field cannot be touched, but will be set to 0 later when __munlock_folio()
>  returns the page to "LRU".  Races prohibit mlock_count from being set to 1 then:
>  rather than risk stranding a page indefinitely as unevictable, always err with
>  mlock_count on the low side, so that when munlocked the page will be rescued to