Messages in this thread | | | Date | Thu, 21 Sep 2023 17:31:47 +0800 | Subject | Re: [PATCH v4 4/8] hugetlb: perform vmemmap restoration on a list of pages | From | Muchun Song <> |
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On 2023/9/21 09:12, Mike Kravetz wrote: > On 09/20/23 11:03, Muchun Song wrote: >>> On Sep 20, 2023, at 10:56, Muchun Song <muchun.song@linux.dev> wrote: >>>> On Sep 20, 2023, at 04:57, Mike Kravetz <mike.kravetz@oracle.com> wrote: >>>> On 09/19/23 17:52, Muchun Song wrote: >>>>> On 2023/9/19 07:01, Mike Kravetz wrote: >>>>> >>>>> I still think we should free a non-optimized HugeTLB page if we >>>>> encounter an OOM situation instead of continue to restore >>>>> vemmmap pages. Restoring vmemmmap pages will only aggravate >>>>> the OOM situation. The suitable appraoch is to free a non-optimized >>>>> HugeTLB page to satisfy our allocation of vmemmap pages, what's >>>>> your opinion, Mike? >>>> I agree. >>>> >>>> As you mentioned previously, this may complicate this code path a bit. >>>> I will rewrite to make this happen. >>> Maybe we could introduced two list passed to update_and_free_pages_bulk (this >>> will be easy for the callers of it), one is for non-optimized huge page, >>> another is optimized one. In update_and_free_pages_bulk, we could first >>> free those non-optimized huge page, and then restore vemmmap pages for >>> those optimized ones, in which case, the code could be simple. >>> hugetlb_vmemmap_restore_folios() dose not need to add complexity, which >>> still continue to restore vmemmap pages and will stop once we encounter >>> an OOM situation. > I am not sure if passing in optimized and non-optimized lists to > update_and_free_pages_bulk will help much. IIUC, it will almost always > be the case where only one list has entries. Is that mostly accurate?
I think you are right. It will be less helpful since most of pages will be not optimized when HVO is enabled.
>> BTW, maybe we should try again iff there are some non-optimized huge page >> whose vmemmap pages are restored successfully previously and could be freed >> first, then continue to restore the vmemmap pages of the remaining huge pages. >> I think the retry code could be done in update_and_free_pages_bulk() as well. > I came up with a new routine to handle these ENOMEM returns from > hugetlb_vmemmap_restore_folios. I 'think' it handles these situations. > Here is an updated version of this patch. Sorry, diff makes it a bit > hard to read. > > From b13bdccb01730f995191944769f87d0725c289ad Mon Sep 17 00:00:00 2001 > From: Mike Kravetz <mike.kravetz@oracle.com> > Date: Sun, 10 Sep 2023 16:14:50 -0700 > Subject: [PATCH] hugetlb: perform vmemmap restoration on a list of pages > > The routine update_and_free_pages_bulk already performs vmemmap > restoration on the list of hugetlb pages in a separate step. In > preparation for more functionality to be added in this step, create a > new routine hugetlb_vmemmap_restore_folios() that will restore > vmemmap for a list of folios. > > This new routine must provide sufficient feedback about errors and > actual restoration performed so that update_and_free_pages_bulk can > perform optimally. > > Special care must be taken when encountering a ENOMEM error from > hugetlb_vmemmap_restore_folios. We want to continue making as much > forward progress as possible. A new routine bulk_vmemmap_restore_enomem > handles this specific situation. > > Signed-off-by: Mike Kravetz <mike.kravetz@oracle.com> > --- > mm/hugetlb.c | 83 ++++++++++++++++++++++++++++++++++---------- > mm/hugetlb_vmemmap.c | 39 +++++++++++++++++++++ > mm/hugetlb_vmemmap.h | 11 ++++++ > 3 files changed, 115 insertions(+), 18 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 70fedf8682c4..52abe56cf38a 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1834,38 +1834,85 @@ static void update_and_free_hugetlb_folio(struct hstate *h, struct folio *folio, > schedule_work(&free_hpage_work); > } > > -static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list) > +static void bulk_vmemmap_restore_enomem(struct hstate *h, > + struct list_head *list, > + unsigned long restored) > { > struct folio *folio, *t_folio; > - bool clear_dtor = false; > > - /* > - * First allocate required vmemmmap (if necessary) for all folios on > - * list. If vmemmap can not be allocated, we can not free folio to > - * lower level allocator, so add back as hugetlb surplus page. > - * add_hugetlb_folio() removes the page from THIS list. > - * Use clear_dtor to note if vmemmap was successfully allocated for > - * ANY page on the list. > - */ > - list_for_each_entry_safe(folio, t_folio, list, lru) { > - if (folio_test_hugetlb_vmemmap_optimized(folio)) { > + if (restored) { > + /* > + * On ENOMEM error, free any restored hugetlb pages so that > + * restore of the entire list can be retried. > + * The idea is that by freeing hugetlb pages with vmemmap > + * (those previously restored) we will free up memory so that > + * we can allocate vmemmap for more hugetlb pages. > + * We must examine and possibly free EVERY hugetlb page on list > + * in order to call hugetlb_vmemmap_restore_folios again. > + * This is not optimal, but is an error case that should not > + * happen frequently. > + */ > + list_for_each_entry_safe(folio, t_folio, list, lru) > + if (!folio_test_hugetlb_vmemmap_optimized(folio)) { > + list_del(&folio->lru); > + spin_lock_irq(&hugetlb_lock); > + __clear_hugetlb_destructor(h, folio); > + spin_unlock_irq(&hugetlb_lock); > + update_and_free_hugetlb_folio(h, folio, false); > + cond_resched(); > + } > + } else { > + /* > + * In the case where vmemmap was not restored for ANY folios, > + * we loop through them trying to restore individually in the > + * hope that someone elsewhere may free enough memory. > + * If unable to restore a page, the hugetlb page is made a > + * surplus page and removed from the list. > + * If are able to restore vmemmap for one hugetlb page, we free > + * it and quit processing the list to retry the bulk operation. > + */ > + list_for_each_entry_safe(folio, t_folio, list, lru) > if (hugetlb_vmemmap_restore(h, &folio->page)) { > spin_lock_irq(&hugetlb_lock); > add_hugetlb_folio(h, folio, true); > spin_unlock_irq(&hugetlb_lock); > - } else > - clear_dtor = true; > - } > + } else { > + list_del(&folio->lru); > + spin_lock_irq(&hugetlb_lock); > + __clear_hugetlb_destructor(h, folio); > + spin_unlock_irq(&hugetlb_lock); > + update_and_free_hugetlb_folio(h, folio, false); > + break; > + } > } > +} > + > +static void update_and_free_pages_bulk(struct hstate *h, struct list_head *list) > +{ > + int ret; > + unsigned long restored; > + struct folio *folio, *t_folio; > > /* > - * If vmemmmap allocation was performed on any folio above, take lock > - * to clear destructor of all folios on list. This avoids the need to > + * First allocate required vmemmmap (if necessary) for all folios. > + * Carefully handle ENOMEM errors and free up any available hugetlb > + * pages in order to make forward progress. > + */ > +retry: > + ret = hugetlb_vmemmap_restore_folios(h, list, &restored); > + if (ret == -ENOMEM) { > + bulk_vmemmap_restore_enomem(h, list, restored); > + goto retry; > + } > + > + /* > + * If vmemmmap allocation was performed on ANY folio , take lock to > + * clear destructor of all folios on list. This avoids the need to > * lock/unlock for each individual folio. > * The assumption is vmemmap allocation was performed on all or none > * of the folios on the list. This is true expect in VERY rare cases. > */ > - if (clear_dtor) { > + if (restored) { > spin_lock_irq(&hugetlb_lock); > list_for_each_entry(folio, list, lru) > __clear_hugetlb_destructor(h, folio); > diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c > index 4558b814ffab..cc91edbfb68b 100644 > --- a/mm/hugetlb_vmemmap.c > +++ b/mm/hugetlb_vmemmap.c > @@ -480,6 +480,45 @@ int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head) > return ret; > } > > +/** > + * hugetlb_vmemmap_restore_folios - restore vmemmap for every folio on the list. > + * @h: struct hstate. > + * @folio_list: list of folios. > + * @restored: Set to number of folios for which vmemmap was restored > + * successfully if caller passes a non-NULL pointer. > + * > + * Return: %0 if vmemmap exists for all folios on the list. If an error is > + * encountered restoring vmemmap for ANY folio, an error code > + * will be returned to the caller. It is then the responsibility > + * of the caller to check the hugetlb vmemmap optimized flag of > + * each folio to determine if vmemmap was actually restored. > + * Note that processing is stopped when first error is encountered. > + */ > +int hugetlb_vmemmap_restore_folios(const struct hstate *h, > + struct list_head *folio_list, > + unsigned long *restored)
How about changing parameter of @restored to a list_head type which returns the non-optimized (previously) or vmemmap-restored-sucessful huge pages? In which case, the caller could traverse this returned list to free them first like you have implemented in bulk_vmemmap_restore_enomem(), it will be more efficient. The meaning of returned value should also be changed accordingly since update_and_free_pages_bulk() wants to whether there is a vmemmap-optimized huge page being restored sucessfully to determine if it should clear hugetlb flag. So hugetlb_vmemmap_restore_folios() could return how many huge pages being restored successful, if a negative number is returned meaning there is some error in the process of restoring of vmemmap.
Thanks.
> +{ > + unsigned long num_restored; > + struct folio *folio; > + int ret = 0; > + > + num_restored = 0; > + list_for_each_entry(folio, folio_list, lru) { > + if (folio_test_hugetlb_vmemmap_optimized(folio)) { > + ret = hugetlb_vmemmap_restore(h, &folio->page); > + if (ret) > + goto out; > + else > + num_restored++; > + } > + } > + > +out: > + if (*restored) > + *restored = num_restored; > + return ret; > +} > + > /* Return true iff a HugeTLB whose vmemmap should and can be optimized. */ > static bool vmemmap_should_optimize(const struct hstate *h, const struct page *head) > { > diff --git a/mm/hugetlb_vmemmap.h b/mm/hugetlb_vmemmap.h > index c512e388dbb4..bb58453c3cc0 100644 > --- a/mm/hugetlb_vmemmap.h > +++ b/mm/hugetlb_vmemmap.h > @@ -19,6 +19,8 @@ > > #ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP > int hugetlb_vmemmap_restore(const struct hstate *h, struct page *head); > +int hugetlb_vmemmap_restore_folios(const struct hstate *h, > + struct list_head *folio_list, unsigned long *restored); > void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head); > void hugetlb_vmemmap_optimize_folios(struct hstate *h, struct list_head *folio_list); > > @@ -45,6 +47,15 @@ static inline int hugetlb_vmemmap_restore(const struct hstate *h, struct page *h > return 0; > } > > +static inline int hugetlb_vmemmap_restore_folios(const struct hstate *h, > + struct list_head *folio_list, > + unsigned long *restored) > +{ > + if (restored) > + *restored = 0; > + return 0; > +} > + > static inline void hugetlb_vmemmap_optimize(const struct hstate *h, struct page *head) > { > }
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