From: "Huang\, Ying" <ying.huang@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
<linux-kernel@vger.kernel.org>, Michal Hocko <mhocko@suse.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Shaohua Li <shli@kernel.org>, Hugh Dickins <hughd@google.com>,
Minchan Kim <minchan@kernel.org>, Rik van Riel <riel@redhat.com>,
Daniel Jordan <daniel.m.jordan@oracle.com>,
Dan Williams <dan.j.williams@intel.com>
Subject: Re: [PATCH 1/6] swap: Add comments to lock_cluster_or_swap_info()
Date: Sat, 14 Jul 2018 12:07:43 +0800 [thread overview]
Message-ID: <87in5ie9yo.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <3c3a4dce-980d-0405-d269-1da9e62b1344@linux.intel.com> (Dave Hansen's message of "Fri, 13 Jul 2018 03:48:28 -0700")
Dave Hansen <dave.hansen@linux.intel.com> writes:
>> +/*
>> + * At most times, fine grained cluster lock is sufficient to protect
>
> Can we call out those times, please?
To protect si->swap_map[], if HDD, si->lock is used, otherwise cluster
lock is used. "at most times" is ambiguous here, I will fix it.
>> + * the operations on sis->swap_map.
>
> Please be careful with the naming. You can call it 'si' because that's
> what the function argument is named. Or, swap_info_struct because
> that's the struct name. Calling it 'sis' is a bit sloppy, no?
>
>> No need to acquire gross grained
>
> "coarse" is a conventional antonym for "fine".
Sorry for my poor English, will change this.
>> + * sis->lock. But cluster and cluster lock isn't available for HDD,
>> + * so sis->lock will be instead for them.
>> + */
>> static inline struct swap_cluster_info *lock_cluster_or_swap_info(
>> struct swap_info_struct *si,
>> unsigned long offset)
>
> What I already knew was: there are two locks. We use one sometimes and
> the other at other times.
>
> What I don't know is why there are two locks, and the heuristics why we
> choose between them. This comment doesn't help explain the things I
> don't know.
cluster lock is used to protect fields of struct swap_cluster_info, and
si->swap_map[], this is described in comments of struct
swap_cluster_info. si->lock is used to protect other fields of si. If
two locks need to be held, hold si->lock first. This is for non-HDD.
For HDD, there are no cluster, so si->lock is used to protect
si->swap_map[].
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2018-07-14 4:17 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-12 23:36 [PATCH 0/6] swap: THP optimizing refactoring Huang, Ying
2018-07-12 23:36 ` [PATCH 1/6] swap: Add comments to lock_cluster_or_swap_info() Huang, Ying
2018-07-13 10:48 ` Dave Hansen
2018-07-14 4:07 ` Huang, Ying [this message]
2018-07-12 23:36 ` [PATCH 2/6] mm/swapfile.c: Replace some #ifdef with IS_ENABLED() Huang, Ying
2018-07-13 18:38 ` Daniel Jordan
2018-07-13 18:55 ` Daniel Jordan
2018-07-12 23:36 ` [PATCH 3/6] swap: Unify normal/huge code path in swap_page_trans_huge_swapped() Huang, Ying
2018-07-13 20:15 ` Daniel Jordan
2018-07-14 12:53 ` Huang, Ying
2018-07-12 23:36 ` [PATCH 4/6] swap: Unify normal/huge code path in put_swap_page() Huang, Ying
2018-07-12 23:36 ` [PATCH 5/6] swap: Add __swap_entry_free_locked() Huang, Ying
2018-07-12 23:36 ` [PATCH 6/6] swap, put_swap_page: Share more between huge/normal code path Huang, Ying
2018-07-13 20:18 ` Daniel Jordan
2018-07-14 12:57 ` Huang, Ying
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