Messages in this thread | | | Subject | Re: [v4 PATCH 2/2] mm: mempolicy: handle vma with unmovable pages mapped correctly in mbind | From | Yang Shi <> | Date | Mon, 22 Jul 2019 22:35:33 -0700 |
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On 7/22/19 6:02 PM, Andrew Morton wrote: > On Mon, 22 Jul 2019 09:25:09 +0200 Vlastimil Babka <vbabka@suse.cz> wrote: > >>> since there may be pages off LRU temporarily. We should migrate other >>> pages if MPOL_MF_MOVE* is specified. Set has_unmovable flag if some >>> paged could not be not moved, then return -EIO for mbind() eventually. >>> >>> With this change the above test would return -EIO as expected. >>> >>> Cc: Vlastimil Babka <vbabka@suse.cz> >>> Cc: Michal Hocko <mhocko@suse.com> >>> Cc: Mel Gorman <mgorman@techsingularity.net> >>> Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> >> Reviewed-by: Vlastimil Babka <vbabka@suse.cz> > Thanks. > > I'm a bit surprised that this doesn't have a cc:stable. Did we > consider that?
The VM_BUG just happens on 4.9, and it is enabled only by CONFIG_VM. For post-4.9 kernel, this fixes the semantics of mbind which should be not a regression IMHO.
> > Also, is this patch dependent upon "mm: mempolicy: make the behavior > consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified"? > Doesn't look that way..
No, it depends on patch #1.
> > Also, I have a note that you had concerns with "mm: mempolicy: make the > behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were > specified". What is the status now?
Vlastimil had given his Reviewed-by.
> > > From: Yang Shi <yang.shi@linux.alibaba.com> > Subject: mm: mempolicy: make the behavior consistent when MPOL_MF_MOVE* and MPOL_MF_STRICT were specified > > When both MPOL_MF_MOVE* and MPOL_MF_STRICT was specified, mbind() should > try best to migrate misplaced pages, if some of the pages could not be > migrated, then return -EIO. > > There are three different sub-cases: > 1. vma is not migratable > 2. vma is migratable, but there are unmovable pages > 3. vma is migratable, pages are movable, but migrate_pages() fails > > If #1 happens, kernel would just abort immediately, then return -EIO, > after the commit a7f40cfe3b7ada57af9b62fd28430eeb4a7cfcb7 ("mm: mempolicy: > make mbind() return -EIO when MPOL_MF_STRICT is specified"). > > If #3 happens, kernel would set policy and migrate pages with best-effort, > but won't rollback the migrated pages and reset the policy back. > > Before that commit, they behaves in the same way. It'd better to keep > their behavior consistent. But, rolling back the migrated pages and > resetting the policy back sounds not feasible, so just make #1 behave as > same as #3. > > Userspace will know that not everything was successfully migrated (via > -EIO), and can take whatever steps it deems necessary - attempt rollback, > determine which exact page(s) are violating the policy, etc. > > Make queue_pages_range() return 1 to indicate there are unmovable pages or > vma is not migratable. > > The #2 is not handled correctly in the current kernel, the following patch > will fix it. > > Link: http://lkml.kernel.org/r/1561162809-59140-2-git-send-email-yang.shi@linux.alibaba.com > Signed-off-by: Yang Shi <yang.shi@linux.alibaba.com> > Cc: Vlastimil Babka <vbabka@suse.cz> > Cc: Michal Hocko <mhocko@suse.com> > Cc: Mel Gorman <mgorman@techsingularity.net> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org> > --- > > mm/mempolicy.c | 84 +++++++++++++++++++++++++++++++++-------------- > 1 file changed, 60 insertions(+), 24 deletions(-) > > --- a/mm/mempolicy.c~mm-mempolicy-make-the-behavior-consistent-when-mpol_mf_move-and-mpol_mf_strict-were-specified > +++ a/mm/mempolicy.c > @@ -429,11 +429,14 @@ static inline bool queue_pages_required( > } > > /* > - * queue_pages_pmd() has three possible return values: > + * queue_pages_pmd() has four possible return values: > + * 2 - there is unmovable page, and MPOL_MF_MOVE* & MPOL_MF_STRICT were > + * specified. > * 1 - pages are placed on the right node or queued successfully. > * 0 - THP was split. > - * -EIO - is migration entry or MPOL_MF_STRICT was specified and an existing > - * page was already on a node that does not follow the policy. > + * -EIO - is migration entry or only MPOL_MF_STRICT was specified and an > + * existing page was already on a node that does not follow the > + * policy. > */ > static int queue_pages_pmd(pmd_t *pmd, spinlock_t *ptl, unsigned long addr, > unsigned long end, struct mm_walk *walk) > @@ -463,7 +466,7 @@ static int queue_pages_pmd(pmd_t *pmd, s > /* go to thp migration */ > if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) { > if (!vma_migratable(walk->vma)) { > - ret = -EIO; > + ret = 2; > goto unlock; > } > > @@ -488,16 +491,29 @@ static int queue_pages_pte_range(pmd_t * > struct queue_pages *qp = walk->private; > unsigned long flags = qp->flags; > int ret; > + bool has_unmovable = false; > pte_t *pte; > spinlock_t *ptl; > > ptl = pmd_trans_huge_lock(pmd, vma); > if (ptl) { > ret = queue_pages_pmd(pmd, ptl, addr, end, walk); > - if (ret > 0) > + switch (ret) { > + /* THP was split, fall through to pte walk */ > + case 0: > + break; > + /* Pages are placed on the right node or queued successfully */ > + case 1: > return 0; > - else if (ret < 0) > + /* > + * Met unmovable pages, MPOL_MF_MOVE* & MPOL_MF_STRICT > + * were specified. > + */ > + case 2: > + return 1; > + case -EIO: > return ret; > + } > } > > if (pmd_trans_unstable(pmd)) > @@ -519,14 +535,21 @@ static int queue_pages_pte_range(pmd_t * > if (!queue_pages_required(page, qp)) > continue; > if (flags & (MPOL_MF_MOVE | MPOL_MF_MOVE_ALL)) { > - if (!vma_migratable(vma)) > + /* MPOL_MF_STRICT must be specified if we get here */ > + if (!vma_migratable(vma)) { > + has_unmovable |= true; > break; > + } > migrate_page_add(page, qp->pagelist, flags); > } else > break; > } > pte_unmap_unlock(pte - 1, ptl); > cond_resched(); > + > + if (has_unmovable) > + return 1; > + > return addr != end ? -EIO : 0; > } > > @@ -639,7 +662,13 @@ static int queue_pages_test_walk(unsigne > * > * If pages found in a given range are on a set of nodes (determined by > * @nodes and @flags,) it's isolated and queued to the pagelist which is > - * passed via @private.) > + * passed via @private. > + * > + * queue_pages_range() has three possible return values: > + * 1 - there is unmovable page, but MPOL_MF_MOVE* & MPOL_MF_STRICT were > + * specified. > + * 0 - queue pages successfully or no misplaced page. > + * -EIO - there is misplaced page and only MPOL_MF_STRICT was specified. > */ > static int > queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end, > @@ -1182,6 +1211,7 @@ static long do_mbind(unsigned long start > struct mempolicy *new; > unsigned long end; > int err; > + int ret; > LIST_HEAD(pagelist); > > if (flags & ~(unsigned long)MPOL_MF_VALID) > @@ -1243,26 +1273,32 @@ static long do_mbind(unsigned long start > if (err) > goto mpol_out; > > - err = queue_pages_range(mm, start, end, nmask, > + ret = queue_pages_range(mm, start, end, nmask, > flags | MPOL_MF_INVERT, &pagelist); > - if (!err) > - err = mbind_range(mm, start, end, new); > > - if (!err) { > - int nr_failed = 0; > + if (ret < 0) > + err = -EIO; > + else { > + err = mbind_range(mm, start, end, new); > > - if (!list_empty(&pagelist)) { > - WARN_ON_ONCE(flags & MPOL_MF_LAZY); > - nr_failed = migrate_pages(&pagelist, new_page, NULL, > - start, MIGRATE_SYNC, MR_MEMPOLICY_MBIND); > - if (nr_failed) > - putback_movable_pages(&pagelist); > - } > + if (!err) { > + int nr_failed = 0; > > - if (nr_failed && (flags & MPOL_MF_STRICT)) > - err = -EIO; > - } else > - putback_movable_pages(&pagelist); > + if (!list_empty(&pagelist)) { > + WARN_ON_ONCE(flags & MPOL_MF_LAZY); > + nr_failed = migrate_pages(&pagelist, new_page, > + NULL, start, MIGRATE_SYNC, > + MR_MEMPOLICY_MBIND); > + if (nr_failed) > + putback_movable_pages(&pagelist); > + } > + > + if ((ret > 0) || > + (nr_failed && (flags & MPOL_MF_STRICT))) > + err = -EIO; > + } else > + putback_movable_pages(&pagelist); > + } > > up_write(&mm->mmap_sem); > mpol_out: > _
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