linux-kernel - Re: [RFC PATCH 1/1] mm: mark folio accessed in minor fault

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Date: Thu, 21 Dec 2023 09:58:25 +0800
From: Zhaoyang Huang <huangzhaoyang@...il.com>
To: Matthew Wilcox <willy@...radead.org>
Cc: "zhaoyang.huang" <zhaoyang.huang@...soc.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, steve.kang@...soc.com
Subject: Re: [RFC PATCH 1/1] mm: mark folio accessed in minor fault

On Wed, Dec 20, 2023 at 10:14 PM Matthew Wilcox <willy@...radead.org> wrote:
>
> On Wed, Dec 20, 2023 at 06:29:48PM +0800, zhaoyang.huang wrote:
> > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> >
> > Inactive mapped folio will be promoted to active only when it is
> > scanned in shrink_inactive_list, while the vfs folio will do this
> > immidiatly when it is accessed. These will introduce two affections:
> >
> > 1. NR_ACTIVE_FILE is not accurate as expected.
> > 2. Low reclaiming efficiency caused by dummy nactive folio which should
> >    be kept as earlier as shrink_active_list.
> >
> > I would like to suggest mark the folio be accessed in minor fault to
> > solve this situation.
>
> This isn't going to be as effective as you imagine.  Almost all file
> faults are handled through filemap_map_pages().  So I must ask, what
> testing have you done with this patch?
>
> And while you're gathering data, what effect would this patch have on your
> workloads?
Thanks for heads-up, I am out of date for readahead mechanism. My goal
is to have mapped file pages behave like other pages which could be
promoted immediately when they are accessed. I will update the patch
and provide benchmark data in new patch set.

>
> diff --git a/mm/filemap.c b/mm/filemap.c
> index 2e6b1daac6cd..8cecf82dcc5a 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -3418,6 +3418,7 @@ static struct folio *next_uptodate_folio(struct xa_state *xas,
>                 max_idx = DIV_ROUND_UP(i_size_read(mapping->host), PAGE_SIZE);
>                 if (xas->xa_index >= max_idx)
>                         goto unlock;
> +               folio_mark_accessed(folio);
>                 return folio;
>  unlock:
>                 folio_unlock(folio);
>