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From: Zi Yan <ziy@nvidia.com>
To: "Pankaj Raghav (Samsung)" <kernel@pankajraghav.com>
Cc: david@fromorbit.com, djwong@kernel.org, chandan.babu@oracle.com,
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Subject: Re: [PATCH v7 05/11] mm: split a folio in minimum folio order chunks
Date: Fri, 07 Jun 2024 12:58:33 -0400
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In-Reply-To: <20240607145902.1137853-6-kernel@pankajraghav.com>
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 <20240607145902.1137853-6-kernel@pankajraghav.com>
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Content-Type: text/plain

Hi Pankaj,

Can you use ziy@nvidia.com instead of zi.yan@sent.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@kernel.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@kernel.org>
> Signed-off-by: Pankaj Raghav <p.raghav@samsung.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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