From: David Hildenbrand <david@redhat.com>
To: Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Oscar Salvador <osalvador@suse.de>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>
Subject: Re: [RFC 5/5] mm, page_alloc: disable pcplists during page isolation
Date: Wed, 9 Sep 2020 14:57:33 +0200 [thread overview]
Message-ID: <d9114e89-590a-8526-3027-39bab004faea@redhat.com> (raw)
In-Reply-To: <c417a996-67d8-8935-ce57-a5dac4408691@redhat.com>
On 09.09.20 13:44, David Hildenbrand wrote:
> On 09.09.20 13:36, Michal Hocko wrote:
>> On Wed 09-09-20 12:48:54, Vlastimil Babka wrote:
>>> Here's a version that will apply on top of next-20200908. The first 4 patches need no change.
>>>
>>> ----8<----
>>> >From 8febc17272b8e8b378e2e5ea5e76b2616f029c5b Mon Sep 17 00:00:00 2001
>>> From: Vlastimil Babka <vbabka@suse.cz>
>>> Date: Mon, 7 Sep 2020 17:20:39 +0200
>>> Subject: [PATCH] mm, page_alloc: disable pcplists during page isolation
>>>
>>> Page isolation can race with process freeing pages to pcplists in a way that
>>> a page from isolated pageblock can end up on pcplist. This can be fixed by
>>> repeated draining of pcplists, as done by patch "mm/memory_hotplug: drain
>>> per-cpu pages again during memory offline" in [1].
>>>
>>> David and Michal would prefer that this race was closed in a way that callers
>>> of page isolation don't need to care about drain. David suggested disabling
>>> pcplists usage completely during page isolation, instead of repeatedly draining
>>> them.
>>>
>>> To achieve this without adding special cases in alloc/free fastpath, we can use
>>> the same 'trick' as boot pagesets - when pcp->high is 0, any pcplist addition
>>> will be immediately flushed.
>>>
>>> The race can thus be closed by setting pcp->high to 0 and draining pcplists
>>> once in start_isolate_page_range(). The draining will serialize after processes
>>> that already disabled interrupts and read the old value of pcp->high in
>>> free_unref_page_commit(), and processes that have not yet disabled interrupts,
>>> will observe pcp->high == 0 when they are rescheduled, and skip pcplists.
>>> This guarantees no stray pages on pcplists in zones where isolation happens.
>>>
>>> We can use the variable zone->nr_isolate_pageblock (protected by zone->lock)
>>> to detect transitions from 0 to 1 (to change pcp->high to 0 and issue drain)
>>> and from 1 to 0 (to restore original pcp->high and batch values cached in
>>> struct zone). We have to avoid external updates to high and batch by taking
>>> pcp_batch_high_lock. To allow multiple isolations in parallel, change this
>>> lock from mutex to rwsem.
>>>
>>> For callers that pair start_isolate_page_range() with
>>> undo_isolated_page_range() properly, this is transparent. Currently that's
>>> alloc_contig_range(). __offline_pages() doesn't call undo_isolated_page_range()
>>> in the succes case, so it has to be carful to handle restoring pcp->high and batch
>>> and unlocking pcp_batch_high_lock.
>>
>> I was hoping that it would be possible to have this completely hidden
>> inside start_isolate_page_range code path. If we need some sort of
>> disable_pcp_free/enable_pcp_free then it seems like a better fit to have
>> an explicit API for that (the naming would be obviously different
>> because we do not want to call out pcp free lists). I strongly suspect
>> that only the memory hotplug really cares for this hard guanrantee.
>> alloc_contig_range simply goes with EBUSY.
>
> There will be different alloc_contig_range() demands in the future: try
> fast (e.g., loads of small CMA allocations) vs. try hard (e.g.,
> virtio-mem). We can add ways to specify that.
>
A reference to a related discussion regarding the "try fast" use case in
CMA for the future:
https://lkml.kernel.org/r/20200818164934.GF3852332@google.com
--
Thanks,
David / dhildenb
next prev parent reply other threads:[~2020-09-09 14:30 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-07 16:36 [RFC 0/5] disable pcplists during page isolation Vlastimil Babka
2020-09-07 16:36 ` [RFC 1/5] mm, page_alloc: clean up pageset high and batch update Vlastimil Babka
2020-09-10 8:31 ` Oscar Salvador
2020-09-10 8:34 ` Oscar Salvador
2020-09-10 10:47 ` David Hildenbrand
2020-09-17 16:05 ` Vlastimil Babka
2020-09-07 16:36 ` [RFC 2/5] mm, page_alloc: calculate pageset high and batch once per zone Vlastimil Babka
2020-09-10 9:00 ` Oscar Salvador
2020-09-10 10:56 ` David Hildenbrand
2020-09-07 16:36 ` [RFC 3/5] mm, page_alloc(): remove setup_pageset() Vlastimil Babka
2020-09-10 9:23 ` Oscar Salvador
2020-09-10 9:57 ` Oscar Salvador
2020-09-18 9:37 ` Vlastimil Babka
2020-09-10 11:00 ` David Hildenbrand
2020-09-07 16:36 ` [RFC 4/5] mm, page_alloc: cache pageset high and batch in struct zone Vlastimil Babka
2020-09-10 11:30 ` Oscar Salvador
2020-09-18 12:02 ` Vlastimil Babka
2020-09-07 16:36 ` [RFC 5/5] mm, page_alloc: disable pcplists during page isolation Vlastimil Babka
2020-09-09 10:48 ` Vlastimil Babka
2020-09-09 11:36 ` Michal Hocko
2020-09-09 11:44 ` David Hildenbrand
2020-09-09 12:57 ` David Hildenbrand [this message]
2020-09-09 11:55 ` Vlastimil Babka
2020-09-10 10:29 ` David Hildenbrand
2020-09-10 11:05 ` Vlastimil Babka
2020-09-10 12:42 ` David Hildenbrand
2020-09-09 12:53 ` Pavel Tatashin
2020-09-08 18:29 ` [RFC 0/5] " David Hildenbrand
2020-09-09 10:54 ` Vlastimil Babka
2020-09-09 11:27 ` osalvador
2020-09-09 11:29 ` David Hildenbrand
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=d9114e89-590a-8526-3027-39bab004faea@redhat.com \
--to=david@redhat.com \
--cc=iamjoonsoo.kim@lge.com \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mhocko@suse.com \
--cc=osalvador@suse.de \
--cc=pasha.tatashin@soleen.com \
--cc=vbabka@suse.cz \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).