linux-kernel - Re: [PATCH v7 05/11] mm: split a folio in minimum folio order chunks

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Date: Fri, 07 Jun 2024 12:58:33 -0400
From: Zi Yan <ziy@...dia.com>
To: "Pankaj Raghav (Samsung)" <kernel@...kajraghav.com>
Cc: david@...morbit.com, djwong@...nel.org, chandan.babu@...cle.com,
 brauner@...nel.org, akpm@...ux-foundation.org, willy@...radead.org,
 mcgrof@...nel.org, linux-mm@...ck.org, hare@...e.de,
 linux-kernel@...r.kernel.org, yang@...amperecomputing.com,
 linux-xfs@...r.kernel.org, p.raghav@...sung.com,
 linux-fsdevel@...r.kernel.org, hch@....de, gost.dev@...sung.com,
 cl@...amperecomputing.com, john.g.garry@...cle.com
Subject: Re: [PATCH v7 05/11] mm: split a folio in minimum folio order chunks

Hi Pankaj,

Can you use ziy@...dia.com instead of zi.yan@...t.com? Since I just use the latter
to send patches. Thanks.

On 7 Jun 2024, at 10:58, Pankaj Raghav (Samsung) wrote:

> From: Luis Chamberlain <mcgrof@...nel.org>
>
> split_folio() and split_folio_to_list() assume order 0, to support
> minorder for non-anonymous folios, we must expand these to check the
> folio mapping order and use that.
>
> Set new_order to be at least minimum folio order if it is set in
> split_huge_page_to_list() so that we can maintain minimum folio order
> requirement in the page cache.
>
> Update the debugfs write files used for testing to ensure the order
> is respected as well. We simply enforce the min order when a file
> mapping is used.
>
> Signed-off-by: Luis Chamberlain <mcgrof@...nel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@...sung.com>
> ---
>  include/linux/huge_mm.h | 14 ++++++++---
>  mm/huge_memory.c        | 55 ++++++++++++++++++++++++++++++++++++++---
>  2 files changed, 61 insertions(+), 8 deletions(-)
>

<snip>

>
> +int split_folio_to_list(struct folio *folio, struct list_head *list)
> +{
> +	unsigned int min_order = 0;
> +
> +	if (!folio_test_anon(folio)) {
> +		if (!folio->mapping) {
> +			count_vm_event(THP_SPLIT_PAGE_FAILED);

You should only increase this counter when the input folio is a THP, namely
folio_test_pmd_mappable(folio) is true. For other large folios, we will
need a separate counter. Something like MTHP_STAT_FILE_SPLIT_FAILED.
See enum mthp_stat_item in include/linux/huge_mm.h.


--
Best Regards,
Yan, Zi

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