linux-fsdevel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Dan Williams <dan.j.williams@intel.com>
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
	Michal Hocko <mhocko@suse.com>, "hch@lst.de" <hch@lst.de>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"jack@suse.cz" <jack@suse.cz>,
	"ross.zwisler@linux.intel.com" <ross.zwisler@linux.intel.com>
Subject: Re: [PATCH v5 05/11] mm, madvise_inject_error: Let memory_failure() optionally take a page reference
Date: Fri, 13 Jul 2018 17:34:48 -0700	[thread overview]
Message-ID: <CAPcyv4j2M4tSKk-mXPaj1sLGCN6qHNh2iaauKwgciRpmqU8cSw@mail.gmail.com> (raw)
In-Reply-To: <20180713063125.GA10034@hori1.linux.bs1.fc.nec.co.jp>

On Thu, Jul 12, 2018 at 11:31 PM, Naoya Horiguchi
<n-horiguchi@ah.jp.nec.com> wrote:
> Hello Dan,
>
> On Wed, Jul 04, 2018 at 02:40:49PM -0700, Dan Williams wrote:
>> The madvise_inject_error() routine uses get_user_pages() to lookup the
>> pfn and other information for injected error, but it does not release
>> that pin. The assumption is that failed pages should be taken out of
>> circulation.
>>
>> However, for dax mappings it is not possible to take pages out of
>> circulation since they are 1:1 physically mapped as filesystem blocks,
>> or device-dax capacity. They also typically represent persistent memory
>> which has an error clearing capability.
>>
>> In preparation for adding a special handler for dax mappings, shift the
>> responsibility of taking the page reference to memory_failure(). I.e.
>> drop the page reference and do not specify MF_COUNT_INCREASED to
>> memory_failure().
>>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
>> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
>> ---
>>  mm/madvise.c |   18 +++++++++++++++---
>>  1 file changed, 15 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/madvise.c b/mm/madvise.c
>> index 4d3c922ea1a1..b731933dddae 100644
>> --- a/mm/madvise.c
>> +++ b/mm/madvise.c
>> @@ -631,11 +631,13 @@ static int madvise_inject_error(int behavior,
>>
>>
>>       for (; start < end; start += PAGE_SIZE << order) {
>> +             unsigned long pfn;
>>               int ret;
>>
>>               ret = get_user_pages_fast(start, 1, 0, &page);
>>               if (ret != 1)
>>                       return ret;
>> +             pfn = page_to_pfn(page);
>>
>>               /*
>>                * When soft offlining hugepages, after migrating the page
>> @@ -651,17 +653,27 @@ static int madvise_inject_error(int behavior,
>>
>>               if (behavior == MADV_SOFT_OFFLINE) {
>>                       pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
>> -                                             page_to_pfn(page), start);
>> +                                     pfn, start);
>>
>>                       ret = soft_offline_page(page, MF_COUNT_INCREASED);
>>                       if (ret)
>>                               return ret;
>>                       continue;
>>               }
>> +
>>               pr_info("Injecting memory failure for pfn %#lx at process virtual address %#lx\n",
>> -                                             page_to_pfn(page), start);
>> +                             pfn, start);
>> +
>> +             ret = memory_failure(pfn, 0);
>> +
>> +             /*
>> +              * Drop the page reference taken by get_user_pages_fast(). In
>> +              * the absence of MF_COUNT_INCREASED the memory_failure()
>> +              * routine is responsible for pinning the page to prevent it
>> +              * from being released back to the page allocator.
>> +              */
>> +             put_page(page);
>>
>> -             ret = memory_failure(page_to_pfn(page), MF_COUNT_INCREASED);
>
> MF_COUNT_INCREASED means that the page refcount for memory error handling
> is taken by the caller so you don't have to take one inside memory_failure().
> So this code don't keep with the definition, then another refcount can be
> taken in memory_failure() in normal LRU page's case for example.
> As a result the error message "Memory failure: %#lx: %s still referenced by
> %d users\n" will be dumped in page_action().
>
> So if you want to put put_page() in madvise_inject_error(), I think that
>
>                 put_page(page);
>                 ret = memory_failure(pfn, 0);
>
> can be acceptable because the purpose of get_user_pages_fast() here is
> just getting pfn, and the refcount itself is not so important.
> IOW, memory_failure() is called only with pfn which never changes depending
> on the page's status.

Ok, I'll resend with the put_page() moved before memory_failure() to
make it more clear that memory_failure() is responsible for taking its
own reference and that there is no dependency to hold the reference in
madvise_inject_error().

> In production system memory_failure() is called via machine check code
> without taking any pagecount, so I don't think the this injection interface
> is properly mocking the real thing. So I'm feeling that this flag will be
> wiped out at some point.

Ok, makes sense.

  reply	other threads:[~2018-07-14  0:34 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-04 21:40 [PATCH v5 00/11] mm: Teach memory_failure() about ZONE_DEVICE pages Dan Williams
2018-07-04 21:40 ` [PATCH v5 01/11] device-dax: Convert to vmf_insert_mixed and vm_fault_t Dan Williams
2018-07-04 21:40 ` [PATCH v5 02/11] device-dax: Enable page_mapping() Dan Williams
2018-07-04 21:40 ` [PATCH v5 03/11] device-dax: Set page->index Dan Williams
2018-07-04 21:40 ` [PATCH v5 04/11] filesystem-dax: " Dan Williams
2018-07-04 21:40 ` [PATCH v5 05/11] mm, madvise_inject_error: Let memory_failure() optionally take a page reference Dan Williams
2018-07-13  6:31   ` Naoya Horiguchi
2018-07-14  0:34     ` Dan Williams [this message]
2018-07-04 21:40 ` [PATCH v5 06/11] mm, memory_failure: Collect mapping size in collect_procs() Dan Williams
2018-07-13  6:49   ` Naoya Horiguchi
2018-07-04 21:41 ` [PATCH v5 07/11] filesystem-dax: Introduce dax_lock_mapping_entry() Dan Williams
2018-07-05  1:07   ` kbuild test robot
2018-07-05  3:31   ` kbuild test robot
2018-07-05  3:33   ` [PATCH v6] " Dan Williams
2018-09-24 15:57   ` [PATCH v5 07/11] " Barret Rhoden
2018-09-27 11:13     ` Jan Kara
2018-07-04 21:41 ` [PATCH v5 08/11] mm, memory_failure: Teach memory_failure() about dev_pagemap pages Dan Williams
2018-07-13  8:52   ` Naoya Horiguchi
2018-07-14  0:28     ` Dan Williams
2018-07-17  6:36       ` Naoya Horiguchi
2018-07-04 21:41 ` [PATCH v5 09/11] x86/mm/pat: Prepare {reserve, free}_memtype() for "decoy" addresses Dan Williams
2018-07-04 21:41 ` [PATCH v5 10/11] x86/memory_failure: Introduce {set, clear}_mce_nospec() Dan Williams
2018-07-04 21:41 ` [PATCH v5 11/11] libnvdimm, pmem: Restore page attributes when clearing errors Dan Williams
2018-07-13  4:44 ` [PATCH v5 00/11] mm: Teach memory_failure() about ZONE_DEVICE pages Dan Williams

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=CAPcyv4j2M4tSKk-mXPaj1sLGCN6qHNh2iaauKwgciRpmqU8cSw@mail.gmail.com \
    --to=dan.j.williams@intel.com \
    --cc=hch@lst.de \
    --cc=jack@suse.cz \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linux-nvdimm@lists.01.org \
    --cc=mhocko@suse.com \
    --cc=n-horiguchi@ah.jp.nec.com \
    --cc=ross.zwisler@linux.intel.com \
    /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).