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Date: Thu, 5 Dec 2019 13:27:36 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Yang Shi <yang.shi@...ux.alibaba.com>, <fabecassis@...dia.com>,
<mhocko@...e.com>, <cl@...ux.com>, <vbabka@...e.cz>,
<mgorman@...hsingularity.net>, <akpm@...ux-foundation.org>
CC: <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
<stable@...r.kernel.org>
Subject: Re: [v3 PATCH] mm: move_pages: return valid node id in status if the
page is already on the target node
On 12/5/19 10:54 AM, Yang Shi wrote:
> Felix Abecassis reports move_pages() would return random status if the
> pages are already on the target node by the below test program:
>
> ---8<---
>
> int main(void)
> {
> const long node_id = 1;
> const long page_size = sysconf(_SC_PAGESIZE);
> const int64_t num_pages = 8;
>
> unsigned long nodemask = 1 << node_id;
> long ret = set_mempolicy(MPOL_BIND, &nodemask, sizeof(nodemask));
> if (ret < 0)
> return (EXIT_FAILURE);
>
> void **pages = malloc(sizeof(void*) * num_pages);
> for (int i = 0; i < num_pages; ++i) {
> pages[i] = mmap(NULL, page_size, PROT_WRITE | PROT_READ,
> MAP_PRIVATE | MAP_POPULATE | MAP_ANONYMOUS,
> -1, 0);
> if (pages[i] == MAP_FAILED)
> return (EXIT_FAILURE);
> }
>
> ret = set_mempolicy(MPOL_DEFAULT, NULL, 0);
> if (ret < 0)
> return (EXIT_FAILURE);
>
> int *nodes = malloc(sizeof(int) * num_pages);
> int *status = malloc(sizeof(int) * num_pages);
> for (int i = 0; i < num_pages; ++i) {
> nodes[i] = node_id;
> status[i] = 0xd0; /* simulate garbage values */
> }
>
> ret = move_pages(0, num_pages, pages, nodes, status, MPOL_MF_MOVE);
> printf("move_pages: %ld\n", ret);
> for (int i = 0; i < num_pages; ++i)
> printf("status[%d] = %d\n", i, status[i]);
> }
> ---8<---
>
> Then running the program would return nonsense status values:
> $ ./move_pages_bug
> move_pages: 0
> status[0] = 208
> status[1] = 208
> status[2] = 208
> status[3] = 208
> status[4] = 208
> status[5] = 208
> status[6] = 208
> status[7] = 208
>
> This is because the status is not set if the page is already on the
> target node, but move_pages() should return valid status as long as it
> succeeds. The valid status may be errno or node id.
>
> We can't simply initialize status array to zero since the pages may be
> not on node 0. Fix it by updating status with node id which the page is
> already on.
>
> Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move")
> Reported-by: Felix Abecassis <fabecassis@...dia.com>
> Tested-by: Felix Abecassis <fabecassis@...dia.com>
> Suggested-by: Michal Hocko <mhocko@...e.com>
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: <stable@...r.kernel.org> 4.17+
> Signed-off-by: Yang Shi <yang.shi@...ux.alibaba.com>
> ---
> v3: * Adopted the suggestion from Michal.
> v2: * Correted the return value when add_page_for_migration() returns 1.
>
> mm/migrate.c | 24 ++++++++++++++++++------
> 1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/mm/migrate.c b/mm/migrate.c
> index a8f87cb..9c172f4 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -1512,9 +1512,11 @@ static int do_move_pages_to_node(struct mm_struct *mm,
> /*
> * Resolves the given address to a struct page, isolates it from the LRU and
> * puts it to the given pagelist.
> - * Returns -errno if the page cannot be found/isolated or 0 when it has been
> - * queued or the page doesn't need to be migrated because it is already on
> - * the target node
> + * Returns:
> + * errno - if the page cannot be found/isolated
> + * 0 - when it doesn't have to be migrated because it is already on the
> + * target node
> + * 1 - when it has been queued
> */
> static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
> int node, struct list_head *pagelist, bool migrate_all)
> @@ -1553,7 +1555,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
> if (PageHuge(page)) {
> if (PageHead(page)) {
> isolate_huge_page(page, pagelist);
> - err = 0;
> + err = 1;
> }
> } else {
> struct page *head;
> @@ -1563,7 +1565,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
> if (err)
> goto out_putpage;
>
> - err = 0;
> + err = 1;
> list_add_tail(&head->lru, pagelist);
> mod_node_page_state(page_pgdat(head),
> NR_ISOLATED_ANON + page_is_file_cache(head),
> @@ -1578,6 +1580,7 @@ static int add_page_for_migration(struct mm_struct *mm, unsigned long addr,
> put_page(page);
> out:
> up_read(&mm->mmap_sem);
> +
> return err;
> }
>
> @@ -1640,8 +1643,17 @@ static int do_pages_move(struct mm_struct *mm, nodemask_t task_nodes,
> */
> err = add_page_for_migration(mm, addr, current_node,
> &pagelist, flags & MPOL_MF_MOVE_ALL);
> - if (!err)
> +
> + /* The page is already on the target node */
> + if (!err) {
> + err = store_status(status, i, current_node, 1);
> + if (err)
> + goto out_flush;
> continue;
> + /* The page is successfully queued */
Nit: could you move this comment down one line, so that it's clear that it
applies to the "else" branch? Like this:
} else if (err > 0) {
/* The page is successfully queued for migration */
continue;
}
> + } else if (err > 0) {
> + continue;
> + }
>
> err = store_status(status, i, err, 1);
> if (err)
>
Also agree with Christopher's requests, but all of these don't affect the
correct operation of the patch, so you can add:
Reviewed-by: John Hubbard <jhubbard@...dia.com>
thanks,
--
John Hubbard
NVIDIA
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