Re: FAILED: patch "[PATCH] mm/gup: avoid an unnecessary allocation call for" failed to apply to 6.11-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Nov 17, 2024 at 01:19:09PM -0800, John Hubbard wrote:
> On 11/17/24 12:33 PM, gregkh@linuxfoundation.org wrote:
> > 
> > The patch below does not apply to the 6.11-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@vger.kernel.org>.
> > 
> > To reproduce the conflict and resubmit, you may use the following commands:
> > 
> > git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.11.y
> > git checkout FETCH_HEAD
> > git cherry-pick -x 94efde1d15399f5c88e576923db9bcd422d217f2
> > # <resolve conflicts, build, test, etc.>
> > git commit -s
> > git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024111754-stamina-flyer-1e05@gregkh' --subject-prefix 'PATCH 6.11.y' HEAD^..
> > 
> 
> It seems that the last hunk didn't apply because it was just too far away,
> as far as I can tell. I've manually applied it, resulting in the same diffs
> as the original, and did a quick smoke test (boot and ran mm tests).
> 
> Here's the updated version for 6.11.y:
> 
> From: John Hubbard <jhubbard@nvidia.com>
> Date: Sun, 17 Nov 2024 13:08:00 -0800
> Subject: [PATCH] mm/gup: avoid an unnecessary allocation call for
>  FOLL_LONGTERM cases
> X-NVConfidentiality: public
> Cc: John Hubbard <jhubbard@nvidia.com>
> 
> commit 53ba78de064b ("mm/gup: introduce
> check_and_migrate_movable_folios()") created a new constraint on the
> pin_user_pages*() API family: a potentially large internal allocation must
> now occur, for FOLL_LONGTERM cases.
> 
> A user-visible consequence has now appeared: user space can no longer pin
> more than 2GB of memory anymore on x86_64.  That's because, on a 4KB
> PAGE_SIZE system, when user space tries to (indirectly, via a device
> driver that calls pin_user_pages()) pin 2GB, this requires an allocation
> of a folio pointers array of MAX_PAGE_ORDER size, which is the limit for
> kmalloc().
> 
> In addition to the directly visible effect described above, there is also
> the problem of adding an unnecessary allocation.  The **pages array
> argument has already been allocated, and there is no need for a redundant
> **folios array allocation in this case.
> 
> Fix this by avoiding the new allocation entirely.  This is done by
> referring to either the original page[i] within **pages, or to the
> associated folio.  Thanks to David Hildenbrand for suggesting this
> approach and for providing the initial implementation (which I've tested
> and adjusted slightly) as well.
> 
> [jhubbard@nvidia.com]: tweaked the patch to apply to linux-stable/6.11.y
> [jhubbard@nvidia.com: whitespace tweak, per David]
>   Link:
> https://lkml.kernel.org/r/131cf9c8-ebc0-4cbb-b722-22fa8527bf3c@nvidia.com
> [jhubbard@nvidia.com: bypass pofs_get_folio(), per Oscar]
>   Link:
> https://lkml.kernel.org/r/c1587c7f-9155-45be-bd62-1e36c0dd6923@nvidia.com
> Link: https://lkml.kernel.org/r/20241105032944.141488-2-jhubbard@nvidia.com
> Fixes: 53ba78de064b ("mm/gup: introduce check_and_migrate_movable_folios()")
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> Suggested-by: David Hildenbrand <david@redhat.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Oscar Salvador <osalvador@suse.de>
> Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
> Cc: Dave Airlie <airlied@redhat.com>
> Cc: Gerd Hoffmann <kraxel@redhat.com>
> Cc: Matthew Wilcox <willy@infradead.org>
> Cc: Christoph Hellwig <hch@infradead.org>
> Cc: Jason Gunthorpe <jgg@nvidia.com>
> Cc: Peter Xu <peterx@redhat.com>
> Cc: Arnd Bergmann <arnd@arndb.de>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Dongwon Kim <dongwon.kim@intel.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Junxiao Chang <junxiao.chang@intel.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>  mm/gup.c | 114 +++++++++++++++++++++++++++++++++++++------------------
>  1 file changed, 77 insertions(+), 37 deletions(-)
> 
> diff --git a/mm/gup.c b/mm/gup.c
> index 947881ff5e8f..fd3d7900c24b 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -2282,20 +2282,57 @@ struct page *get_dump_page(unsigned long addr)
>  #endif /* CONFIG_ELF_CORE */
> 
>  #ifdef CONFIG_MIGRATION
> +
> +/*
> + * An array of either pages or folios ("pofs"). Although it may seem
> tempting to
> + * avoid this complication, by simply interpreting a list of folios as a
> list of
> + * pages, that approach won't work in the longer term, because eventually
> the
> + * layouts of struct page and struct folio will become completely
> different.
> + * Furthermore, this pof approach avoids excessive page_folio() calls.

Patch is line-wrapped :(

Can you resend it in a format I can apply it in?

thanks,

greg k-h