Messages in this thread | | | Subject | Re: [v3 PATCH] mm: move_pages: return valid node id in status if the page is already on the target node | From | Yang Shi <> | Date | Thu, 5 Dec 2019 14:00:31 -0800 |
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On 12/5/19 1:27 PM, John Hubbard wrote: > 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@nvidia.com> >> Tested-by: Felix Abecassis <fabecassis@nvidia.com> >> Suggested-by: Michal Hocko <mhocko@suse.com> >> Cc: John Hubbard <jhubbard@nvidia.com> >> Cc: Christoph Lameter <cl@linux.com> >> Cc: Vlastimil Babka <vbabka@suse.cz> >> Cc: Mel Gorman <mgorman@techsingularity.net> >> Cc: <stable@vger.kernel.org> 4.17+ >> Signed-off-by: Yang Shi <yang.shi@linux.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; > }
Sure.
> > >> + } 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@nvidia.com> > > thanks,
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