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Message-ID: <0b66c1f8-c694-7971-b2d3-e1dd53a0f103@nvidia.com>
Date: Mon, 12 Aug 2019 15:21:49 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Ira Weiny <ira.weiny@...el.com>
CC: Andrew Morton <akpm@...ux-foundation.org>,
Christoph Hellwig <hch@...radead.org>,
Dan Williams <dan.j.williams@...el.com>,
Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.cz>,
Jason Gunthorpe <jgg@...pe.ca>,
Jérôme Glisse <jglisse@...hat.com>,
LKML <linux-kernel@...r.kernel.org>, <linux-mm@...ck.org>,
<linux-fsdevel@...r.kernel.org>, <linux-rdma@...r.kernel.org>
Subject: Re: [RFC PATCH 2/2] mm/gup: introduce vaddr_pin_pages_remote()
On 8/12/19 3:03 PM, Ira Weiny wrote:
> On Sun, Aug 11, 2019 at 06:50:44PM -0700, john.hubbard@...il.com wrote:
>> From: John Hubbard <jhubbard@...dia.com>
...
>> +/**
>> + * vaddr_pin_pages pin pages by virtual address and return the pages to the
>
> vaddr_pin_pages_remote
>
> Fixed in my tree.
thanks. :)
>
>> + * user.
>> + *
>> + * @tsk: the task_struct to use for page fault accounting, or
>> + * NULL if faults are not to be recorded.
>> + * @mm: mm_struct of target mm
>> + * @addr: start address
>> + * @nr_pages: number of pages to pin
>> + * @gup_flags: flags to use for the pin
>> + * @pages: array of pages returned
>> + * @vaddr_pin: initialized meta information this pin is to be associated
>> + * with.
>> + *
>> + * This is the "vaddr_pin_pages" corresponding variant to
>> + * get_user_pages_remote(), but with FOLL_PIN semantics: the implementation sets
>> + * FOLL_PIN. That, in turn, means that the pages must ultimately be released
>> + * by put_user_page().
>> + */
>> +long vaddr_pin_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
>> + unsigned long start, unsigned long nr_pages,
>> + unsigned int gup_flags, struct page **pages,
>> + struct vm_area_struct **vmas, int *locked,
>> + struct vaddr_pin *vaddr_pin)
>> +{
>> + gup_flags |= FOLL_TOUCH | FOLL_REMOTE | FOLL_PIN;
>> +
>> + return __get_user_pages_locked(tsk, mm, start, nr_pages, pages, vmas,
>> + locked, gup_flags, vaddr_pin);
>> +}
>> +EXPORT_SYMBOL(vaddr_pin_pages_remote);
>> +
>> /**
>> * vaddr_unpin_pages_dirty_lock - counterpart to vaddr_pin_pages
>> *
>> @@ -2536,3 +2568,21 @@ void vaddr_unpin_pages_dirty_lock(struct page **pages, unsigned long nr_pages,
>> __put_user_pages_dirty_lock(vaddr_pin, pages, nr_pages, make_dirty);
>> }
>> EXPORT_SYMBOL(vaddr_unpin_pages_dirty_lock);
>> +
>> +/**
>> + * vaddr_unpin_pages - simple, non-dirtying counterpart to vaddr_pin_pages
>> + *
>> + * @pages: array of pages returned
>> + * @nr_pages: number of pages in pages
>> + * @vaddr_pin: same information passed to vaddr_pin_pages
>> + *
>> + * Like vaddr_unpin_pages_dirty_lock, but for non-dirty pages. Useful in putting
>> + * back pages in an error case: they were never made dirty.
>> + */
>> +void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
>> + struct vaddr_pin *vaddr_pin)
>> +{
>> + __put_user_pages_dirty_lock(vaddr_pin, pages, nr_pages, false);
>> +}
>> +EXPORT_SYMBOL(vaddr_unpin_pages);
>
> Rather than have another wrapping call why don't we just do this? Would it be
> so bad to just have to specify false for make_dirty?
Sure, passing in false for make_dirty is fine, and in fact, there may even be
error cases I've forgotten about that *want* to dirty the page.
I thought about these variants, and realized that we don't generally need to
say "lock" anymore, because we're going to forcibly use set_page_dirty_lock
(rather than set_page_dirty) in this part of the code. And a shorter name
is nice. Since you've dropped both "_dirty" and "_lock" from the function
name, it's still nice and short even though we pass in make_dirty as an arg.
So that's a long-winded, "the API below looks good to me". :)
>
>
> diff --git a/mm/gup.c b/mm/gup.c
> index e77b250c1307..ca660a5e8206 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2540,7 +2540,7 @@ long vaddr_pin_pages_remote(struct task_struct *tsk, struct mm_struct *mm,
> EXPORT_SYMBOL(vaddr_pin_pages_remote);
>
> /**
> - * vaddr_unpin_pages_dirty_lock - counterpart to vaddr_pin_pages
> + * vaddr_unpin_pages - counterpart to vaddr_pin_pages
> *
> * @pages: array of pages returned
> * @nr_pages: number of pages in pages
> @@ -2551,26 +2551,9 @@ EXPORT_SYMBOL(vaddr_pin_pages_remote);
> * in vaddr_pin_pages should be passed back into this call for proper
> * tracking.
> */
> -void vaddr_unpin_pages_dirty_lock(struct page **pages, unsigned long nr_pages,
> - struct vaddr_pin *vaddr_pin, bool make_dirty)
> +void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
> + struct vaddr_pin *vaddr_pin, bool make_dirty)
> {
> __put_user_pages_dirty_lock(vaddr_pin, pages, nr_pages, make_dirty);
> }
> EXPORT_SYMBOL(vaddr_unpin_pages_dirty_lock);
> -
> -/**
> - * vaddr_unpin_pages - simple, non-dirtying counterpart to vaddr_pin_pages
> - *
> - * @pages: array of pages returned
> - * @nr_pages: number of pages in pages
> - * @vaddr_pin: same information passed to vaddr_pin_pages
> - *
> - * Like vaddr_unpin_pages_dirty_lock, but for non-dirty pages. Useful in putting
> - * back pages in an error case: they were never made dirty.
> - */
> -void vaddr_unpin_pages(struct page **pages, unsigned long nr_pages,
> - struct vaddr_pin *vaddr_pin)
> -{
> - __put_user_pages_dirty_lock(vaddr_pin, pages, nr_pages, false);
> -}
> -EXPORT_SYMBOL(vaddr_unpin_pages);
>
thanks,
--
John Hubbard
NVIDIA
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