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Date: Tue, 10 Jul 2018 09:08:42 +0800 From: "Huang\, Ying" <ying.huang@...el.com> To: Dave Hansen <dave.hansen@...ux.intel.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>, "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andrea Arcangeli <aarcange@...hat.com>, Michal Hocko <mhocko@...e.com>, Johannes Weiner <hannes@...xchg.org>, "Shaohua Li" <shli@...nel.org>, Hugh Dickins <hughd@...gle.com>, Minchan Kim <minchan@...nel.org>, Rik van Riel <riel@...hat.com>, Naoya Horiguchi <n-horiguchi@...jp.nec.com>, Zi Yan <zi.yan@...rutgers.edu>, Daniel Jordan <daniel.m.jordan@...cle.com> Subject: Re: [PATCH -mm -v4 01/21] mm, THP, swap: Enable PMD swap operations for CONFIG_THP_SWAP Dave Hansen <dave.hansen@...ux.intel.com> writes: > On 06/21/2018 08:51 PM, Huang, Ying wrote: >> From: Huang Ying <ying.huang@...el.com> >> >> 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 > config option (CONFIG_ARCH_ENABLE_THP_MIGRATION). > > But, we also need them for THP swap. > ... > > It would also be nice to explain a bit why you are moving code around. This looks much better than my original words. Thanks for help! > Would this look any better if we made a Kconfig option: > > config HAVE_THP_SWAP_ENTRIES > def_bool n > # "Swap entries" in the page tables are used > # both for migration and actual swap. > depends on THP_SWAP || ARCH_ENABLE_THP_MIGRATION > > 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. Because both you and Dan thinks it's better to add new Kconfig option, I will do that. Best Regards, Huang, Ying
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