linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: David Hildenbrand <david@redhat.com>
To: Alexander Duyck <alexander.h.duyck@linux.intel.com>,
	Alexander Duyck <alexander.duyck@gmail.com>,
	kvm@vger.kernel.org, mst@redhat.com,
	linux-kernel@vger.kernel.org, willy@infradead.org,
	mhocko@kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org,
	mgorman@techsingularity.net, vbabka@suse.cz
Cc: yang.zhang.wz@gmail.com, nitesh@redhat.com,
	konrad.wilk@oracle.com, pagupta@redhat.com, riel@surriel.com,
	lcapitulino@redhat.com, dave.hansen@intel.com,
	wei.w.wang@intel.com, aarcange@redhat.com, pbonzini@redhat.com,
	dan.j.williams@intel.com, osalvador@suse.de
Subject: Re: [PATCH v15 3/7] mm: Add function __putback_isolated_page
Date: Tue, 17 Dec 2019 11:58:13 +0100	[thread overview]
Message-ID: <8a4b0337-0bad-2978-32e8-6f90c7365f00@redhat.com> (raw)
In-Reply-To: <9eb9173278370dd604c4cefd30ed10be36600854.camel@linux.intel.com>

On 16.12.19 17:22, Alexander Duyck wrote:
> On Mon, 2019-12-16 at 12:36 +0100, David Hildenbrand wrote:
>> [...]
>>> +/**
>>> + * __putback_isolated_page - Return a now-isolated page back where we got it
>>> + * @page: Page that was isolated
>>> + * @order: Order of the isolated page
>>> + *
>>> + * This function is meant to return a page pulled from the free lists via
>>> + * __isolate_free_page back to the free lists they were pulled from.
>>> + */
>>> +void __putback_isolated_page(struct page *page, unsigned int order)
>>> +{
>>> +	struct zone *zone = page_zone(page);
>>> +	unsigned long pfn;
>>> +	unsigned int mt;
>>> +
>>> +	/* zone lock should be held when this function is called */
>>> +	lockdep_assert_held(&zone->lock);
>>> +
>>> +	pfn = page_to_pfn(page);
>>> +	mt = get_pfnblock_migratetype(page, pfn);
>>
>> IMHO get_pageblock_migratetype() would be nicer - I guess the compiler
>> will optimize out the double page_to_pfn().
> 
> The thing is I need the page_to_pfn call already in order to pass the
> value to __free_one_page. With that being the case why not juse use
> get_pfnblock_migratetype?

I was reading
	set_pageblock_migratetype(page, migratetype);
And wondered why we don't use straight forward
	get_pageblock_migratetype()
but instead something that looks like a micro-optimization

> 
> Also there are some scenarios where __page_to_pfn is not that simple a
> call with us having to get the node ID so we can find the pgdat structure
> to perform the calculation. I'm not sure the compiler would be ble to
> figure out that the result is the same for both calls, so it is better to
> make it explicit.

Only in case of CONFIG_SPARSEMEM we have to go via the section - but I
doubt this is really worth optimizing here.

But yeah, I'm fine with this change, only "IMHO
get_pageblock_migratetype() would be nicer" :)

> 
>>> +
>>> +	/* Return isolated page to tail of freelist. */
>>> +	__free_one_page(page, pfn, zone, order, mt);
>>> +}
>>> +
>>>  /*
>>>   * Update NUMA hit/miss statistics
>>>   *
>>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>>> index 04ee1663cdbe..d93d2be0070f 100644
>>> --- a/mm/page_isolation.c
>>> +++ b/mm/page_isolation.c
>>> @@ -134,13 +134,11 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>>>  		__mod_zone_freepage_state(zone, nr_pages, migratetype);
>>>  	}
>>>  	set_pageblock_migratetype(page, migratetype);
>>> +	if (isolated_page)
>>> +		__putback_isolated_page(page, order);
>>>  	zone->nr_isolate_pageblock--;
>>>  out:
>>>  	spin_unlock_irqrestore(&zone->lock, flags);
>>> -	if (isolated_page) {
>>> -		post_alloc_hook(page, order, __GFP_MOVABLE);
>>> -		__free_pages(page, order);
>>> -	}
>>
>> So If I get it right:
>>
>> post_alloc_hook() does quite some stuff like
>> - arch_alloc_page(page, order);
>> - kernel_map_pages(page, 1 << order, 1)
>> - kasan_alloc_pages()
>> - kernel_poison_pages(1)
>> - set_page_owner()
>>
>> Which free_pages_prepare() will undo, like
>> - reset_page_owner()
>> - kernel_poison_pages(0)
>> - arch_free_page()
>> - kernel_map_pages()
>> - kasan_free_nondeferred_pages()
>>
>> Both would be skipped now - which sounds like the right thing to do IMHO
>> (and smells like quite a performance improvement). I haven't verified if
>> actually everything we skip in free_pages_prepare() is safe (I think it
>> is, it seems to be mostly relevant for actually used/allocated pages).
> 
> That was kind of my thought on this. Basically the logic I was following
> was that the code path will call move_freepages_block that bypasses all of
> the above mentioned calls if the pages it is moving will not be merged. If
> it is safe in that case my assumption is that it should be safe to just
> call __putback_isolated_page in such a case as it also bypasses the block
> above, but it supports merging the page with other pages that are already
> on the freelist.

Makes sense to me

Acked-by: David Hildenbrand <david@redhat.com>


-- 
Thanks,

David / dhildenb


  reply	other threads:[~2019-12-17 10:58 UTC|newest]

Thread overview: 39+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-05 16:22 [PATCH v15 0/7] mm / virtio: Provide support for free page reporting Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 1/7] mm: Adjust shuffle code to allow for future coalescing Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 2/7] mm: Use zone and order instead of free area in free_list manipulators Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 3/7] mm: Add function __putback_isolated_page Alexander Duyck
2019-12-16 11:36   ` David Hildenbrand
2019-12-16 16:22     ` Alexander Duyck
2019-12-17 10:58       ` David Hildenbrand [this message]
2019-12-17 16:26         ` Alexander Duyck
2019-12-17 17:24           ` David Hildenbrand
2019-12-17 18:24             ` Alexander Duyck
2019-12-17 18:46               ` David Hildenbrand
2019-12-17 21:50                 ` Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 4/7] mm: Introduce Reported pages Alexander Duyck
2019-12-16 10:17   ` Nitesh Narayan Lal
2019-12-16 16:28     ` Alexander Duyck
2019-12-17  8:55       ` Nitesh Narayan Lal
2019-12-17 16:31         ` Alexander Duyck
2019-12-18  7:31           ` Mel Gorman
2019-12-16 11:44   ` Nitesh Narayan Lal
2019-12-16 16:10     ` Alexander Duyck
2019-12-05 16:22 ` [PATCH v15 5/7] virtio-balloon: Pull page poisoning config out of free page hinting Alexander Duyck
2019-12-13  7:03   ` Michael S. Tsirkin
2019-12-05 16:22 ` [PATCH v15 6/7] virtio-balloon: Add support for providing free page reports to host Alexander Duyck
2019-12-13  7:08   ` Michael S. Tsirkin
2019-12-13 16:35     ` Alexander Duyck
2019-12-15  9:29       ` Michael S. Tsirkin
2019-12-13 10:15   ` David Hildenbrand
2019-12-13 16:37     ` Alexander Duyck
2019-12-05 16:23 ` [PATCH v15 7/7] mm: Add free page reporting documentation Alexander Duyck
2019-12-05 16:24 ` [PATCH v15 QEMU 1/3] virtio-ballon: Implement support for page poison tracking feature Alexander Duyck
2019-12-05 16:24 ` [PATCH v15 QEMU 2/3] virtio-balloon: Add bit to notify guest of unused page reporting Alexander Duyck
2019-12-05 16:24 ` [PATCH v15 QEMU 3/3] virtio-balloon: Provide a interface for " Alexander Duyck
2019-12-05 16:26 ` [PATCH v15 QEMU 4/3 RFC] memory: Add support for MADV_FREE as mechanism to lazy discard pages Alexander Duyck
2019-12-12 23:47 ` [PATCH v15 0/7] mm / virtio: Provide support for free page reporting Alexander Duyck
2019-12-13 10:00 ` David Hildenbrand
2019-12-13 11:08   ` Mel Gorman
2019-12-13 16:59     ` Alexander Duyck
2019-12-13 16:46   ` Alexander Duyck
2019-12-16 12:21     ` 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=8a4b0337-0bad-2978-32e8-6f90c7365f00@redhat.com \
    --to=david@redhat.com \
    --cc=aarcange@redhat.com \
    --cc=akpm@linux-foundation.org \
    --cc=alexander.duyck@gmail.com \
    --cc=alexander.h.duyck@linux.intel.com \
    --cc=dan.j.williams@intel.com \
    --cc=dave.hansen@intel.com \
    --cc=konrad.wilk@oracle.com \
    --cc=kvm@vger.kernel.org \
    --cc=lcapitulino@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=mgorman@techsingularity.net \
    --cc=mhocko@kernel.org \
    --cc=mst@redhat.com \
    --cc=nitesh@redhat.com \
    --cc=osalvador@suse.de \
    --cc=pagupta@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=riel@surriel.com \
    --cc=vbabka@suse.cz \
    --cc=wei.w.wang@intel.com \
    --cc=willy@infradead.org \
    --cc=yang.zhang.wz@gmail.com \
    --subject='Re: [PATCH v15 3/7] mm: Add function __putback_isolated_page' \
    /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

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).