Commit 0139aa7b authored by Joonsoo Kim's avatar Joonsoo Kim Committed by Linus Torvalds
Browse files

mm: rename _count, field of the struct page, to _refcount 



Many developers already know that field for reference count of the
struct page is _count and atomic type.  They would try to handle it
directly and this could break the purpose of page reference count
tracepoint.  To prevent direct _count modification, this patch rename it
to _refcount and add warning message on the code.  After that, developer
who need to handle reference count will find that field should not be
accessed directly.

[akpm@linux-foundation.org: fix comments, per Vlastimil]
[akpm@linux-foundation.org: Documentation/vm/transhuge.txt too]
[sfr@canb.auug.org.au: sync ethernet driver changes]
Signed-off-by: default avatarJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: default avatarStephen Rothwell <sfr@canb.auug.org.au>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Sunil Goutham <sgoutham@cavium.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Manish Chopra <manish.chopra@qlogic.com>
Cc: Yuval Mintz <yuval.mintz@qlogic.com>
Cc: Tariq Toukan <tariqt@mellanox.com>
Cc: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 6d061f9f

Documentation/vm/transhuge.txt

+5 −5
Original line number Diff line number Diff line
@@ -394,9 +394,9 @@ hugepage natively. Once finished you can drop the page table lock. 
Refcounting on THP is mostly consistent with refcounting on other compound

pages:



  - get_page()/put_page() and GUP operate in head page's ->_count.

  - get_page()/put_page() and GUP operate in head page's ->_refcount.



  - ->_count in tail pages is always zero: get_page_unless_zero() never

  - ->_refcount in tail pages is always zero: get_page_unless_zero() never

    succeed on tail pages.



  - map/unmap of the pages with PTE entry increment/decrement ->_mapcount
@@ -426,15 +426,15 @@ requests to split pinned huge page: it expects page count to be equal to 
sum of mapcount of all sub-pages plus one (split_huge_page caller must

have reference for head page).



split_huge_page uses migration entries to stabilize page->_count and

split_huge_page uses migration entries to stabilize page->_refcount and

page->_mapcount.



We safe against physical memory scanners too: the only legitimate way

scanner can get reference to a page is get_page_unless_zero().



All tail pages has zero ->_count until atomic_add(). It prevent scanner

All tail pages has zero ->_refcount until atomic_add(). It prevent scanner

from geting reference to tail page up to the point. After the atomic_add()

we don't care about ->_count value.  We already known how many references

we don't care about ->_refcount value.  We already known how many references

with should uncharge from head page.



For head page get_page_unless_zero() will succeed and we don't mind. It's

arch/tile/mm/init.c

+1 −1
Original line number Diff line number Diff line
@@ -679,7 +679,7 @@ static void __init init_free_pfn_range(unsigned long start, unsigned long end) 
			 * Hacky direct set to avoid unnecessary

			 * lock take/release for EVERY page here.

			 */

			p->_count.counter = 0;

			p->_refcount.counter = 0;

			p->_mapcount.counter = -1;

		}

		init_page_count(page);

drivers/block/aoe/aoecmd.c

+1 −1
Original line number Diff line number Diff line
@@ -861,7 +861,7 @@ rqbiocnt(struct request *r) 
 * discussion.

 *

 * We cannot use get_page in the workaround, because it insists on a

 * positive page count as a precondition.  So we use _count directly.

 * positive page count as a precondition.  So we use _refcount directly.

 */

static void

bio_pageinc(struct bio *bio)

drivers/hwtracing/intel_th/msu.c

+1 −1
Original line number Diff line number Diff line
@@ -1164,7 +1164,7 @@ static void msc_mmap_close(struct vm_area_struct *vma) 
	if (!atomic_dec_and_mutex_lock(&msc->mmap_count, &msc->buf_mutex))

		return;



	/* drop page _counts */

	/* drop page _refcounts */

	for (pg = 0; pg < msc->nr_pages; pg++) {

		struct page *page = msc_buffer_get_page(msc, pg);

drivers/net/ethernet/mellanox/mlx5/core/en_rx.c

+10 −10
Original line number Diff line number Diff line
@@ -433,8 +433,8 @@ static int mlx5e_alloc_rx_fragmented_mpwqe(struct mlx5e_rq *rq, 
	for (i = 0; i < MLX5_MPWRQ_PAGES_PER_WQE; i++) {

		if (unlikely(mlx5e_alloc_and_map_page(rq, wi, i)))

			goto err_unmap;

		atomic_add(mlx5e_mpwqe_strides_per_page(rq),

			   &wi->umr.dma_info[i].page->_count);

		page_ref_add(wi->umr.dma_info[i].page,

			     mlx5e_mpwqe_strides_per_page(rq));

		wi->skbs_frags[i] = 0;

	}
@@ -452,8 +452,8 @@ err_unmap: 
	while (--i >= 0) {

		dma_unmap_page(rq->pdev, wi->umr.dma_info[i].addr, PAGE_SIZE,

			       PCI_DMA_FROMDEVICE);

		atomic_sub(mlx5e_mpwqe_strides_per_page(rq),

			   &wi->umr.dma_info[i].page->_count);

		page_ref_sub(wi->umr.dma_info[i].page,

			     mlx5e_mpwqe_strides_per_page(rq));

		put_page(wi->umr.dma_info[i].page);

	}

	dma_unmap_single(rq->pdev, wi->umr.mtt_addr, mtt_sz, PCI_DMA_TODEVICE);
@@ -477,8 +477,8 @@ void mlx5e_free_rx_fragmented_mpwqe(struct mlx5e_rq *rq, 
	for (i = 0; i < MLX5_MPWRQ_PAGES_PER_WQE; i++) {

		dma_unmap_page(rq->pdev, wi->umr.dma_info[i].addr, PAGE_SIZE,

			       PCI_DMA_FROMDEVICE);

		atomic_sub(mlx5e_mpwqe_strides_per_page(rq) - wi->skbs_frags[i],

			   &wi->umr.dma_info[i].page->_count);

		page_ref_sub(wi->umr.dma_info[i].page,

			mlx5e_mpwqe_strides_per_page(rq) - wi->skbs_frags[i]);

		put_page(wi->umr.dma_info[i].page);

	}

	dma_unmap_single(rq->pdev, wi->umr.mtt_addr, mtt_sz, PCI_DMA_TODEVICE);
@@ -527,8 +527,8 @@ static int mlx5e_alloc_rx_linear_mpwqe(struct mlx5e_rq *rq, 
	 */

	split_page(wi->dma_info.page, MLX5_MPWRQ_WQE_PAGE_ORDER);

	for (i = 0; i < MLX5_MPWRQ_PAGES_PER_WQE; i++) {

		atomic_add(mlx5e_mpwqe_strides_per_page(rq),

			   &wi->dma_info.page[i]._count);

		page_ref_add(&wi->dma_info.page[i],

			     mlx5e_mpwqe_strides_per_page(rq));

		wi->skbs_frags[i] = 0;

	}
@@ -551,8 +551,8 @@ void mlx5e_free_rx_linear_mpwqe(struct mlx5e_rq *rq, 
	dma_unmap_page(rq->pdev, wi->dma_info.addr, rq->wqe_sz,

		       PCI_DMA_FROMDEVICE);

	for (i = 0; i < MLX5_MPWRQ_PAGES_PER_WQE; i++) {

		atomic_sub(mlx5e_mpwqe_strides_per_page(rq) - wi->skbs_frags[i],

			   &wi->dma_info.page[i]._count);

		page_ref_sub(&wi->dma_info.page[i],

			mlx5e_mpwqe_strides_per_page(rq) - wi->skbs_frags[i]);

		put_page(&wi->dma_info.page[i]);

	}

}

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