From: "Huang\, Ying" <ying.huang@intel.com>
To: Dave Hansen <dave.hansen@linux.intel.com>,
Andrew Morton <akpm@linux-foundation.org>
Cc: <linux-mm@kvack.org>, <linux-kernel@vger.kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
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>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Zi Yan <zi.yan@cs.rutgers.edu>,
Daniel Jordan <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH -mm -v4 05/21] mm, THP, swap: Support PMD swap mapping in free_swap_and_cache()/swap_free()
Date: Tue, 10 Jul 2018 15:13:58 +0800 [thread overview]
Message-ID: <87y3ejh8ax.fsf@yhuang-dev.intel.com> (raw)
In-Reply-To: <49178f48-6635-353c-678d-3db436d3f9c3@linux.intel.com> (Dave Hansen's message of "Mon, 9 Jul 2018 10:19:25 -0700")
Dave Hansen <dave.hansen@linux.intel.com> writes:
> I'm seeing a pattern here.
>
> old code:
>
> foo()
> {
> do_swap_something()
> }
>
> new code:
>
> foo(bool cluster)
> {
> if (cluster)
> do_swap_cluster_something();
> else
> do_swap_something();
> }
>
> That make me fear that we have:
> 1. Created a new, wholly untested code path
> 2. Created two places to patch bugs
> 3. Are not reusing code when possible
>
> The code non-resuse was, and continues to be, IMNHO, one of the largest
> sources of bugs with the original THP implementation. It might be
> infeasible to do here, but let's at least give it as much of a go as we can.
I totally agree that we should unify the code path for huge and normal
page/swap if possible. One concern is code size for !CONFIG_THP_SWAP.
The original method is good for that. The new method may introduce some
huge swap related code that is hard to be eliminated for
!CONFIG_THP_SWAP. Andrew Morton pointed this out for the patchset of
the first step of the THP swap optimization.
This may be mitigated at least partly via,
`
#ifdef CONFIG_THP_SWAP
#define nr_swap_entries(nr) (nr)
#else
#define nr_swap_entries(nr) 1
#endif
void do_something(swp_entry_t entry, int __nr_entries)
{
int i, nr_entries = nr_swap_entries(__nr_entries);
if (nr_entries = SWAPFILE_CLUSTER)
; /* huge swap specific */
else
; /* normal swap specific */
for (i = 0; i < nr_entries; i++) {
; /* do something for each entry */
}
/* ... */
}
`
and rely on compiler to do the dirty work for us if possible.
Hi, Andrew,
What do you think about this?
> Can I ask that you take another round through this set and:
>
> 1. Consolidate code refactoring into separate patches
Sure.
> 2. Add comments to code, and avoid doing it solely in changelogs
Sure.
> 3. Make an effort to share more code between the old code and new
> code. Where code can not be shared, call that out in the changelog.
Will do that if we resolve the code size concern.
> This is a *really* hard-to-review set at the moment. Doing those things
> will make it much easier to review and hopefully give us more
> maintainable code going forward.
>
> My apologies for not having done this review sooner.
Thanks a lot for your comments!
Best Regards,
Huang, Ying
next prev parent reply other threads:[~2018-07-10 7:14 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-22 3:51 [PATCH -mm -v4 00/21] mm, THP, swap: Swapout/swapin THP in one piece Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 01/21] mm, THP, swap: Enable PMD swap operations for CONFIG_THP_SWAP Huang, Ying
2018-07-07 21:11 ` Dan Williams
2018-07-09 5:40 ` Huang, Ying
2018-07-09 6:08 ` Dan Williams
2018-07-09 6:34 ` Huang, Ying
2018-07-09 15:59 ` Dave Hansen
2018-07-10 1:08 ` Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 02/21] mm, THP, swap: Make CONFIG_THP_SWAP depends on CONFIG_SWAP Huang, Ying
2018-07-07 21:12 ` Dan Williams
2018-07-09 6:34 ` Huang, Ying
2018-07-09 16:00 ` Dave Hansen
2018-07-10 1:19 ` Huang, Ying
2018-07-10 1:59 ` Dave Hansen
2018-07-10 5:26 ` Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 03/21] mm, THP, swap: Support PMD swap mapping in swap_duplicate() Huang, Ying
2018-06-29 6:04 ` Matthew Wilcox
2018-07-02 5:19 ` Huang, Ying
2018-07-07 23:22 ` Dan Williams
2018-07-09 7:38 ` Huang, Ying
2018-07-09 16:51 ` Dave Hansen
2018-07-10 6:44 ` Huang, Ying
2018-07-10 13:50 ` Dave Hansen
2018-07-11 0:59 ` Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 04/21] mm, THP, swap: Support PMD swap mapping in swapcache_free_cluster() Huang, Ying
2018-07-09 17:11 ` Dave Hansen
2018-07-10 6:53 ` Huang, Ying
2018-07-10 13:54 ` Dave Hansen
2018-07-11 1:08 ` Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 05/21] mm, THP, swap: Support PMD swap mapping in free_swap_and_cache()/swap_free() Huang, Ying
2018-07-05 18:33 ` Daniel Jordan
2018-07-06 12:49 ` Huang, Ying
2018-07-09 17:19 ` Dave Hansen
2018-07-10 7:13 ` Huang, Ying [this message]
2018-07-10 14:07 ` Dave Hansen
2018-07-11 1:28 ` Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 06/21] mm, THP, swap: Support PMD swap mapping when splitting huge PMD Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 07/21] mm, THP, swap: Support PMD swap mapping in split_swap_cluster() Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 08/21] mm, THP, swap: Support to read a huge swap cluster for swapin a THP Huang, Ying
2018-06-29 6:21 ` Matthew Wilcox
2018-07-02 6:02 ` Huang, Ying
2018-07-04 0:12 ` Daniel Jordan
2018-07-04 2:24 ` Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 09/21] mm, THP, swap: Swapin a THP as a whole Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 10/21] mm, THP, swap: Support to count THP swapin and its fallback Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 11/21] mm, THP, swap: Add sysfs interface to configure THP swapin Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 12/21] mm, THP, swap: Support PMD swap mapping in swapoff Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 13/21] mm, THP, swap: Support PMD swap mapping in madvise_free() Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 14/21] mm, cgroup, THP, swap: Support to move swap account for PMD swap mapping Huang, Ying
2018-07-09 17:20 ` Daniel Jordan
2018-07-10 7:49 ` Huang, Ying
2018-07-10 22:49 ` Daniel Jordan
2018-06-22 3:51 ` [PATCH -mm -v4 15/21] mm, THP, swap: Support to copy PMD swap mapping when fork() Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 16/21] mm, THP, swap: Free PMD swap mapping when zap_huge_pmd() Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 17/21] mm, THP, swap: Support PMD swap mapping for MADV_WILLNEED Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 18/21] mm, THP, swap: Support PMD swap mapping in mincore() Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 19/21] mm, THP, swap: Support PMD swap mapping in common path Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 20/21] mm, THP, swap: create PMD swap mapping when unmap the THP Huang, Ying
2018-06-22 3:51 ` [PATCH -mm -v4 21/21] mm, THP: Avoid to split THP when reclaim MADV_FREE THP Huang, Ying
2018-06-28 4:51 ` [PATCH -mm -v4 00/21] mm, THP, swap: Swapout/swapin THP in one piece Andrew Morton
2018-06-28 5:29 ` Huang, Ying
2018-06-28 5:31 ` Andrew Morton
2018-06-28 5:35 ` Huang, Ying
2018-06-28 6:18 ` Andrew Morton
2018-06-28 9:03 ` Matthew Wilcox
2018-06-29 1:17 ` Huang, Ying
2018-06-29 5:57 ` Matthew Wilcox
2018-07-02 5:19 ` Huang, Ying
2018-07-04 2:11 ` Sergey Senozhatsky
2018-07-04 2:20 ` Huang, Ying
2018-07-04 2:27 ` Sergey Senozhatsky
2018-07-04 2:59 ` Huang, Ying
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