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From:   Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
To:     David Hildenbrand <david@redhat.com>
CC:     Naoya Horiguchi <nao.horiguchi@gmail.com>,
        "linux-mm@kvack.org" <linux-mm@kvack.org>,
        Michal Hocko <mhocko@kernel.org>,
        Oscar Salvador <osalvador@suse.de>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH] mm, soft-offline: convert parameter to pfn
Thread-Topic: [PATCH] mm, soft-offline: convert parameter to pfn
Thread-Index: AQHVhLrXcCLS8WnGfEC5psVxf+kROqdd3rQA
Date:   Thu, 17 Oct 2019 07:50:18 +0000
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On Thu, Oct 17, 2019 at 09:16:42AM +0200, David Hildenbrand wrote:
> On 17.10.19 01:47, Naoya Horiguchi wrote:
> > On Wed, Oct 16, 2019 at 10:57:57AM +0200, David Hildenbrand wrote:
> > > On 16.10.19 10:54, Naoya Horiguchi wrote:
> > > > On Wed, Oct 16, 2019 at 10:34:52AM +0200, David Hildenbrand wrote:
> > > > > On 16.10.19 10:27, Naoya Horiguchi wrote:
> > > > > > On Wed, Oct 16, 2019 at 09:56:19AM +0200, David Hildenbrand wrote:
> > > > > > > On 16.10.19 09:09, Naoya Horiguchi wrote:
> > > > > > > > Hi,
> > > > > > > > 
> > > > > > > > I wrote a simple cleanup for parameter of soft_offline_page(),
> > > > > > > > based on thread https://lkml.org/lkml/2019/10/11/57.
> > > > > > > > 
> > > > > > > > I know that we need more cleanup on hwpoison-inject, but I think
> > > > > > > > that will be mentioned in re-write patchset Oscar is preparing now.
> > > > > > > > So let me shared only this part as a separate one now.
> > > > > > ...
> > > > > > > 
> > > > > > > I think you should rebase that patch on linux-next (where the
> > > > > > > pfn_to_online_page() check is in place). I assume you'll want to move the
> > > > > > > pfn_to_online_page() check into soft_offline_page() then as well?
> > > > > > 
> > > > > > I rebased to next-20191016. And yes, we will move pfn_to_online_page()
> > > > > > into soft offline code.  It seems that we can also move pfn_valid(),
> > > > > > but is simply moving like below good enough for you?
> > > > > 
> > > > > At least I can't am the patch to current next/master (due to
> > > > > pfn_to_online_page()).
> > > 
> > > Could also be that my "git am" skills failed as the mail was not a
> > > proper patch itself :)
> > 
> > Sorry for the inconvenience, my company email system breaks original
> > message by introducing quoted-printable format ('=20' or '=3D').
> > Most mail client usually handles it but git-am doesn't.
> > I give up using it and send via smtp.gmail.com.
> > 
> > > > @@ -1877,11 +1877,17 @@ static int soft_offline_free_page(struct page *page)
> > > >    * This is not a 100% solution for all memory, but tries to be
> > > >    * ``good enough'' for the majority of memory.
> > > >    */
> > > > -int soft_offline_page(struct page *page, int flags)
> > > > +int soft_offline_page(unsigned long pfn, int flags)
> > > >   {
> > > >   	int ret;
> > > > -	unsigned long pfn = page_to_pfn(page);
> > > > +	struct page *page;
> > > > +	if (!pfn_valid(pfn))
> > > > +		return -ENXIO;
> > > > +	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
> > > > +	page = pfn_to_online_page(pfn);
> > > > +	if (!page)
> > > > +		return -EIO;
> > > >   	if (is_zone_device_page(page)) {
> > > 
> > > -> this is now no longer possible! So you can drop the whole if
> > > (is_zone_device....) case
> > 
> > OK, thanks. I updated it.
> > 
> > Thanks,
> > Naoya Horiguchi
> > ---
> >  From 5faf227839b578726fe7f5ff414a153abb3b3a31 Mon Sep 17 00:00:00 2001
> > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Date: Thu, 17 Oct 2019 08:40:53 +0900
> > Subject: [PATCH] mm, soft-offline: convert parameter to pfn
> > 
> > Currently soft_offline_page() receives struct page, and its sibling
> > memory_failure() receives pfn. This discrepancy looks weird and makes
> > precheck on pfn validity tricky. So let's align them.
> > 
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > ---
> >   drivers/base/memory.c |  7 +------
> >   include/linux/mm.h    |  2 +-
> >   mm/madvise.c          |  2 +-
> >   mm/memory-failure.c   | 19 +++++++++----------
> >   4 files changed, 12 insertions(+), 18 deletions(-)
> > 
> > diff --git a/drivers/base/memory.c b/drivers/base/memory.c
> > index 55907c27075b..a757d9ed88a7 100644
> > --- a/drivers/base/memory.c
> > +++ b/drivers/base/memory.c
> > @@ -538,12 +538,7 @@ static ssize_t soft_offline_page_store(struct device *dev,
> >   	if (kstrtoull(buf, 0, &pfn) < 0)
> >   		return -EINVAL;
> >   	pfn >>= PAGE_SHIFT;
> > -	if (!pfn_valid(pfn))
> > -		return -ENXIO;
> > -	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
> > -	if (!pfn_to_online_page(pfn))
> > -		return -EIO;
> > -	ret = soft_offline_page(pfn_to_page(pfn), 0);
> > +	ret = soft_offline_page(pfn, 0);
> >   	return ret == 0 ? count : ret;
> >   }
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index 44d058723db9..fd360d208346 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -2794,7 +2794,7 @@ extern int sysctl_memory_failure_early_kill;
> >   extern int sysctl_memory_failure_recovery;
> >   extern void shake_page(struct page *p, int access);
> >   extern atomic_long_t num_poisoned_pages __read_mostly;
> > -extern int soft_offline_page(struct page *page, int flags);
> > +extern int soft_offline_page(unsigned long pfn, int flags);
> >   /*
> > diff --git a/mm/madvise.c b/mm/madvise.c
> > index 2be9f3fdb05e..99dd06fecfa9 100644
> > --- a/mm/madvise.c
> > +++ b/mm/madvise.c
> > @@ -887,7 +887,7 @@ static int madvise_inject_error(int behavior,
> >   			pr_info("Soft offlining pfn %#lx at process virtual address %#lx\n",
> >   					pfn, start);
> > -			ret = soft_offline_page(page, MF_COUNT_INCREASED);
> > +			ret = soft_offline_page(pfn, MF_COUNT_INCREASED);
> >   			if (ret)
> >   				return ret;
> >   			continue;
> > diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> > index 05c8c6df25e6..af2712004a4d 100644
> > --- a/mm/memory-failure.c
> > +++ b/mm/memory-failure.c
> > @@ -1476,7 +1476,7 @@ static void memory_failure_work_func(struct work_struct *work)
> >   		if (!gotten)
> >   			break;
> >   		if (entry.flags & MF_SOFT_OFFLINE)
> > -			soft_offline_page(pfn_to_page(entry.pfn), entry.flags);
> > +			soft_offline_page(entry.pfn, entry.flags);
> >   		else
> >   			memory_failure(entry.pfn, entry.flags);
> >   	}
> > @@ -1857,7 +1857,7 @@ static int soft_offline_free_page(struct page *page)
> >   /**
> >    * soft_offline_page - Soft offline a page.
> > - * @page: page to offline
> > + * @pfn: pfn to soft-offline
> >    * @flags: flags. Same as memory_failure().
> >    *
> >    * Returns 0 on success, otherwise negated errno.
> > @@ -1877,18 +1877,17 @@ static int soft_offline_free_page(struct page *page)
> >    * This is not a 100% solution for all memory, but tries to be
> >    * ``good enough'' for the majority of memory.
> >    */
> > -int soft_offline_page(struct page *page, int flags)
> > +int soft_offline_page(unsigned long pfn, int flags)
> >   {
> >   	int ret;
> > -	unsigned long pfn = page_to_pfn(page);
> > +	struct page *page;
> > -	if (is_zone_device_page(page)) {
> > -		pr_debug_ratelimited("soft_offline: %#lx page is device page\n",
> > -				pfn);
> > -		if (flags & MF_COUNT_INCREASED)
> > -			put_page(page);
> > +	if (!pfn_valid(pfn))
> > +		return -ENXIO;
> > +	/* Only online pages can be soft-offlined (esp., not ZONE_DEVICE). */
> > +	page = pfn_to_online_page(pfn);
> > +	if (!page)
> 
> If you pass in a PFN with MF_COUNT_INCREASED via mm/madvise.c, you would now
> no longer do a put_page(page) in case of ZONE_DEVICE (!page =
> pfn_to_online_page(pfn);)

Yes, right.

> 
> something like this
> 
> page = pfn_to_online_page(pfn);
> if (!page) {
> 	/*
> 	 * With MF_COUNT_INCREASED, we can use pfn_to_page() directly
> 	 * (esp., ZONE_DEVICE).
> 	 */
> 	if (flags & MF_COUNT_INCREASED)
> 		put_page(pfn_to_page(page));
> 	return -EIO;
> }
> 
> For !pfn_valid(pfn), this is not relevant.

Actually I guess that !pfn_valid() never happens when called from
madvise_inject_error(), because madvise_inject_error() gets pfn via
get_user_pages_fast() which only returns valid page for valid pfn.

And we plan to remove MF_COUNT_INCREASED by Oscar's re-design work,
so I start feeling that this patch should come on top of his tree.

Thanks,
Naoya Horiguchi