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SubjectRe: [PATCH -mm -v4 01/21] mm, THP, swap: Enable PMD swap operations for CONFIG_THP_SWAP
On 06/21/2018 08:51 PM, Huang, Ying wrote:
> From: Huang Ying <>
> Previously, the PMD swap operations are only enabled for
> CONFIG_ARCH_ENABLE_THP_MIGRATION. Because they are only used by the
> THP migration support. We will support PMD swap mapping to the huge
> swap cluster and swapin the THP as a whole. That will be enabled via
> CONFIG_THP_SWAP and needs these PMD swap operations. So enable the
> PMD swap operations for CONFIG_THP_SWAP too.

This commit message kinda skirts around the real reasons for this patch.
Shouldn't we just say something like:

Currently, "swap entries" in the page tables are used for a
number of things outside of actual swap, like page migration.
We support THP/PMD "swap entries" for page migration currently
and the functions behind this are tied to page migration's

But, we also need them for THP swap.

It would also be nice to explain a bit why you are moving code around.

Would this look any better if we made a Kconfig option:

def_bool n
# "Swap entries" in the page tables are used
# both for migration and actual swap.

You logically talked about this need for PMD swap operations in your
commit message, so I think it makes sense to codify that in a single
place where it can be coherently explained.

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