From: Michal Hocko <mhocko@kernel.org>
To: Joonsoo Kim <js1304@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
kernel-team@lge.com, Vlastimil Babka <vbabka@suse.cz>,
Christoph Hellwig <hch@infradead.org>,
Roman Gushchin <guro@fb.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [PATCH v3 5/8] mm/migrate: make a standard migration target allocation function
Date: Mon, 29 Jun 2020 10:03:50 +0200 [thread overview]
Message-ID: <20200629080350.GB32461@dhcp22.suse.cz> (raw)
In-Reply-To: <CAAmzW4PT+M8mUwXMPhQSKLhz9nkPATivL5D-yLyyfC9SOwPnYQ@mail.gmail.com>
On Mon 29-06-20 15:41:37, Joonsoo Kim wrote:
> 2020년 6월 26일 (금) 오후 4:33, Michal Hocko <mhocko@kernel.org>님이 작성:
> >
> > On Fri 26-06-20 14:02:49, Joonsoo Kim wrote:
> > > 2020년 6월 25일 (목) 오후 9:05, Michal Hocko <mhocko@kernel.org>님이 작성:
> > > >
> > > > On Tue 23-06-20 15:13:45, Joonsoo Kim wrote:
> > [...]
> > > > > -struct page *new_page_nodemask(struct page *page,
> > > > > - int preferred_nid, nodemask_t *nodemask)
> > > > > +struct page *alloc_migration_target(struct page *page, unsigned long private)
> > > > > {
> > > > > - gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL;
> > > > > + struct migration_target_control *mtc;
> > > > > + gfp_t gfp_mask;
> > > > > unsigned int order = 0;
> > > > > struct page *new_page = NULL;
> > > > > + int zidx;
> > > > > +
> > > > > + mtc = (struct migration_target_control *)private;
> > > > > + gfp_mask = mtc->gfp_mask;
> > > > >
> > > > > if (PageHuge(page)) {
> > > > > return alloc_huge_page_nodemask(
> > > > > - page_hstate(compound_head(page)),
> > > > > - preferred_nid, nodemask, 0, false);
> > > > > + page_hstate(compound_head(page)), mtc->nid,
> > > > > + mtc->nmask, gfp_mask, false);
> > > > > }
> > > > >
> > > > > if (PageTransHuge(page)) {
> > > > > + gfp_mask &= ~__GFP_RECLAIM;
> > > >
> > > > What's up with this gfp_mask modification?
> > >
> > > THP page allocation uses a standard gfp masks, GFP_TRANSHUGE_LIGHT and
> > > GFP_TRANHUGE. __GFP_RECLAIM flags is a big part of this standard mask design.
> > > So, I clear it here so as not to disrupt the THP gfp mask.
> >
> > Why this wasn't really needed before? I guess I must be missing
> > something here. This patch should be mostly mechanical convergence of
> > existing migration callbacks but this change adds a new behavior AFAICS.
>
> Before this patch, a user cannot specify a gfp_mask and THP allocation
> uses GFP_TRANSHUGE
> statically.
Unless I am misreading there are code paths (e.g.new_page_nodemask) which simply use
add GFP_TRANSHUGE to GFP_USER | __GFP_MOVABLE | __GFP_RETRY_MAYFAIL. And
this goes all the way to thp migration introduction.
> After this patch, a user can specify a gfp_mask and it
> could conflict with GFP_TRANSHUGE.
> This code tries to avoid this conflict.
>
> > It would effectively drop __GFP_RETRY_MAYFAIL and __GFP_KSWAPD_RECLAIM
>
> __GFP_RETRY_MAYFAIL isn't dropped. __GFP_RECLAIM is
> "___GFP_DIRECT_RECLAIM|___GFP_KSWAPD_RECLAIM".
> So, __GFP_KSWAPD_RECLAIM would be dropped for THP allocation.
> IIUC, THP allocation doesn't use __GFP_KSWAPD_RECLAIM since it's
> overhead is too large and this overhead should be given to the caller
> rather than system thread (kswapd) and so on.
Yes, there is a reason why KSWAPD is excluded from THP allocations in
the page fault path. Maybe we want to extend that behavior to the
migration as well. I do not have a strong opinion on that because I
haven't seen excessive kswapd reclaim due to THP migrations. They are
likely too rare.
But as I've said in my previous email. Make this a separate patch with
an explanation why we want this.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2020-06-29 8:03 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-23 6:13 [PATCH v3 0/8] clean-up the migration target allocation functions js1304
2020-06-23 6:13 ` [PATCH v3 1/8] mm/page_isolation: prefer the node of the source page js1304
2020-06-23 6:13 ` [PATCH v3 2/8] mm/migrate: move migration helper from .h to .c js1304
2020-06-23 6:13 ` [PATCH v3 3/8] mm/hugetlb: unify migration callbacks js1304
2020-06-24 21:18 ` Mike Kravetz
2020-06-25 11:26 ` Michal Hocko
2020-06-26 4:02 ` Joonsoo Kim
2020-07-02 16:13 ` Vlastimil Babka
2020-07-03 0:55 ` Joonsoo Kim
2020-06-23 6:13 ` [PATCH v3 4/8] mm/hugetlb: make hugetlb migration callback CMA aware js1304
2020-06-25 11:54 ` Michal Hocko
2020-06-26 4:49 ` Joonsoo Kim
2020-06-26 7:23 ` Michal Hocko
2020-06-29 6:27 ` Joonsoo Kim
2020-06-29 7:55 ` Michal Hocko
2020-06-30 6:30 ` Joonsoo Kim
2020-06-30 6:42 ` Michal Hocko
2020-06-30 7:22 ` Joonsoo Kim
2020-06-30 16:37 ` Mike Kravetz
2020-06-23 6:13 ` [PATCH v3 5/8] mm/migrate: make a standard migration target allocation function js1304
2020-06-25 12:05 ` Michal Hocko
2020-06-26 5:02 ` Joonsoo Kim
2020-06-26 7:33 ` Michal Hocko
2020-06-29 6:41 ` Joonsoo Kim
2020-06-29 8:03 ` Michal Hocko [this message]
2020-06-30 7:19 ` Joonsoo Kim
2020-07-03 15:25 ` Vlastimil Babka
2020-06-23 6:13 ` [PATCH v3 6/8] mm/gup: use a standard migration target allocation callback js1304
2020-06-25 12:08 ` Michal Hocko
2020-06-26 5:03 ` Joonsoo Kim
2020-07-03 15:56 ` Vlastimil Babka
2020-07-06 8:34 ` Joonsoo Kim
2020-06-23 6:13 ` [PATCH v3 7/8] mm/mempolicy: " js1304
2020-06-25 12:09 ` Michal Hocko
2020-07-03 15:59 ` Vlastimil Babka
[not found] ` <20200708012044.GC992@lca.pw>
2020-07-08 6:45 ` Michal Hocko
2020-10-08 3:21 ` Hugh Dickins
2020-10-08 17:29 ` Mike Kravetz
2020-10-09 5:50 ` Hugh Dickins
2020-10-09 17:42 ` Mike Kravetz
2020-10-09 22:23 ` Hugh Dickins
2020-10-10 0:25 ` Mike Kravetz
2020-06-23 6:13 ` [PATCH v3 8/8] mm/page_alloc: remove a wrapper for alloc_migration_target() js1304
2020-06-25 12:10 ` Michal Hocko
2020-07-03 16:18 ` Vlastimil Babka
2020-07-06 8:44 ` Joonsoo Kim
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