Hi Kirill Tkhai, Please see mm/vmscan.c in which it first added to list and than throw the error : -------------------------------------------------------------------------------------------------- keep: list_add(&page->lru, &ret_pages); VM_BUG_ON_PAGE(PageLRU(page) || PageUnevictable(page), page); ---------------------------------------------------------------------------------------------------
Before throwing error, pages are added to list, this is under iteration of shrink_page_list(). From: Kirill Tkhai <ktk...@virtuozzo.com> Sent: 18 March 2019 15:03:15 To: Pankaj Suryawanshi; Vlastimil Babka; Michal Hocko; aneesh.ku...@linux.ibm.com Cc: linux-kernel@vger.kernel.org; minc...@kernel.org; linux...@kvack.org; khand...@linux.vnet.ibm.com; hillf...@alibaba-inc.com Subject: Re: [External] Re: vmscan: Reclaim unevictable pages Hi, Pankaj, On 18.03.2019 12:09, Pankaj Suryawanshi wrote: > > Hello > > shrink_page_list() returns , number of pages reclaimed, when pages is > unevictable it returns VM_BUG_ON_PAGE(PageLRU(page) || > PageUnevicatble(page),page); the general idea is shrink_page_list() can't iterate PageUnevictable() pages. PageUnevictable() pages are never being added to lists, which shrink_page_list() uses for iteration. Also, a page can't be marked as PageUnevictable(), when it's attached to a shrinkable list. So, the problem should be somewhere outside shrink_page_list(). I won't suggest you something about CMA, since I haven't dived in that code. > We can add the unevictable pages in reclaim list in shrink_page_list(), > return total number of reclaim pages including unevictable pages, let the > caller handle unevictable pages. > > I think the problem is shrink_page_list is awkard. If page is unevictable it > goto activate_locked->keep_locked->keep lables, keep lable list_add the > unevictable pages and throw the VM_BUG instead of passing it to caller while > it relies on caller for non-reclaimed-non-unevictable page's putback. > I think we can make it consistent so that shrink_page_list could return > non-reclaimed pages via page_list and caller can handle it. As an advance, it > could try to migrate mlocked pages without retrial. > > > Below is the issue of CMA_ALLOC of large size buffer : (Kernel version - > 4.14.65 (On Android pie [ARM])). > > [ 24.718792] page dumped because: VM_BUG_ON_PAGE(PageLRU(page) || > PageUnevictable(page)) > [ 24.726949] page->mem_cgroup:bd008c00 > [ 24.730693] ------------[ cut here ]------------ > [ 24.735304] kernel BUG at mm/vmscan.c:1350! > [ 24.739478] Internal error: Oops - BUG: 0 [#1] PREEMPT SMP ARM > > > Below is the patch which solved this issue : > > diff --git a/mm/vmscan.c b/mm/vmscan.c > index be56e2e..12ac353 100644 > --- a/mm/vmscan.c > +++ b/mm/vmscan.c > @@ -998,7 +998,7 @@ static unsigned long shrink_page_list(struct list_head > *page_list, > sc->nr_scanned++; > > if (unlikely(!page_evictable(page))) > - goto activate_locked; > + goto cull_mlocked; > > if (!sc->may_unmap && page_mapped(page)) > goto keep_locked; > @@ -1331,7 +1331,12 @@ static unsigned long shrink_page_list(struct list_head > *page_list, > } else > list_add(&page->lru, &free_pages); > continue; > - > +cull_mlocked: > + if (PageSwapCache(page)) > + try_to_free_swap(page); > + unlock_page(page); > + list_add(&page->lru, &ret_pages); > + continue; > activate_locked: > /* Not a candidate for swapping, so reclaim swap space. */ > if (PageSwapCache(page) && (mem_cgroup_swap_full(page) || > > > > > It fixes the below issue. > > 1. Large size buffer allocation using cma_alloc successful with unevictable > pages. > > cma_alloc of current kernel will fail due to unevictable page > > Please let me know if anything i am missing. > > Regards, > Pankaj > > From: Vlastimil Babka <vba...@suse.cz> > Sent: 18 March 2019 14:12:50 > To: Pankaj Suryawanshi; Kirill Tkhai; Michal Hocko; aneesh.ku...@linux.ibm.com > Cc: linux-kernel@vger.kernel.org; minc...@kernel.org; linux...@kvack.org; > khand...@linux.vnet.ibm.com; hillf...@alibaba-inc.com > Subject: Re: [External] Re: vmscan: Reclaim unevictable pages > > > On 3/15/19 11:11 AM, Pankaj Suryawanshi wrote: >> >> [ cc Aneesh kumar, Anshuman, Hillf, Vlastimil] > > Can you send a proper patch with changelog explaining the change? I > don't know the context of this thread. > >> From: Pankaj Suryawanshi >> Sent: 15 March 2019 11:35:05 >> To: Kirill Tkhai; Michal Hocko >> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org; linux...@kvack.org >> Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages >> >> >> >> [ cc linux-mm ] >> >> >> From: Pankaj Suryawanshi >> Sent: 14 March 2019 19:14:40 >> To: Kirill Tkhai; Michal Hocko >> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org >> Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages >> >> >> >> Hello , >> >> Please ignore the curly braces, they are just for debugging. >> >> Below is the updated patch. >> >> >> diff --git a/mm/vmscan.c b/mm/vmscan.c >> index be56e2e..12ac353 100644 >> --- a/mm/vmscan.c >> +++ b/mm/vmscan.c >> @@ -998,7 +998,7 @@ static unsigned long shrink_page_list(struct list_head >> *page_list, >> sc->nr_scanned++; >> >> if (unlikely(!page_evictable(page))) >> - goto activate_locked; >> + goto cull_mlocked; >> >> if (!sc->may_unmap && page_mapped(page)) >> goto keep_locked; >> @@ -1331,7 +1331,12 @@ static unsigned long shrink_page_list(struct >> list_head *page_list, >> } else >> list_add(&page->lru, &free_pages); >> continue; >> - >> +cull_mlocked: >> + if (PageSwapCache(page)) >> + try_to_free_swap(page); >> + unlock_page(page); >> + list_add(&page->lru, &ret_pages); >> + continue; >> activate_locked: >> /* Not a candidate for swapping, so reclaim swap space. */ >> if (PageSwapCache(page) && (mem_cgroup_swap_full(page) || >> >> >> >> Regards, >> Pankaj >> >> >> From: Kirill Tkhai <ktk...@virtuozzo.com> >> Sent: 14 March 2019 14:55:34 >> To: Pankaj Suryawanshi; Michal Hocko >> Cc: linux-kernel@vger.kernel.org; minc...@kernel.org >> Subject: Re: Re: [External] Re: vmscan: Reclaim unevictable pages >> >> >> On 14.03.2019 11:52, Pankaj Suryawanshi wrote: >>> >>> I am using kernel version 4.14.65 (on Android pie [ARM]). >>> >>> No additional patches applied on top of vanilla.(Core MM). >>> >>> If I change in the vmscan.c as below patch, it will work. >> >> Sorry, but 4.14.65 does not have braces around trylock_page(), >> like in your patch below. >> >> See >> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/mm/vmscan.c?h=v4.14.65 >> >> [...] >> >>>> diff --git a/mm/vmscan.c b/mm/vmscan.c >>>> index be56e2e..2e51edc 100644 >>>> --- a/mm/vmscan.c >>>> +++ b/mm/vmscan.c >>>> @@ -990,15 +990,17 @@ static unsigned long shrink_page_list(struct >>>> list_head *page_list, >>>> page = lru_to_page(page_list); >>>> list_del(&page->lru); >>>> >>>> if (!trylock_page(page)) { >>>> goto keep; >>>> } >> >> ************************************************************************************************************************************************************* >> eInfochips Business Disclaimer: This e-mail message and all attachments >> transmitted with it are intended solely for the use of the addressee and >> may contain legally privileged and confidential information. 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