Messages in this thread | | | Date | Wed, 4 Feb 2009 08:44:08 +0900 | From | MinChan Kim <> | Subject | Re: [PATCH v2] fix mlocked page counter mistmatch |
| |
On Wed, Feb 04, 2009 at 01:44:52AM +0900, KOSAKI Motohiro wrote: > Hi MinChan, > > I'm confusing now. > Can you teach me?
No problem. :)
> > > When I tested following program, I found that mlocked counter > > is strange. > > It couldn't free some mlocked pages of test program. > > It is caused that try_to_unmap_file don't check real > > page mapping in vmas. > > What meanining is "real" page mapping?
What I mean is that if the page is mapped at the vma, I call it's "real" page mapping. I explain it more detaily below.
> > > > That's because goal of address_space for file is to find all processes > > into which the file's specific interval is mapped. > > What I mean is that it's not related page but file's interval. > > hmmm. No. > I ran your reproduce program. > > two vma pointing the same page cause this leaking.
I don't think so.
> > iow, any library have .text and .data segment. then the tail of .text > and the head of .data vma point the same page. > its page was leaked. > > > > Even if the page isn't really mapping at the vma, it returns > > SWAP_MLOCK since the vma have VM_LOCKED, then calls > > try_to_mlock_page. After all, mlocked counter is increased again. > > > > COWed anon page in a file-backed vma could be a such case. > > This patch resolves it. > > What meaning is "anon page in a file-backed"? > As far as I know, if cow happend on private mapping page, new page is > treated truth anon. >
vm_area_struct's annotation can explain about your question.
struct vm_area_struct { struct mm_struct * vm_mm; /* The address space we belong to. */ .... .... /* * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma * list, after a COW of one of the file pages. A MAP_SHARED vma * can only be in the i_mmap tree. An anonymous MAP_PRIVATE, stack * or brk vma (with NULL file) can only be in an anon_vma list. */ struct list_head anon_vma_node; /* Serialized by anon_vma->lock */ struct anon_vma *anon_vma; /* Serialized by page_table_lock */ .... .... }
Let us call it anon page in a file-backed. In this case, the new page is mapped at the vma. the vma don't include old page any more but i_mmap tree still have the vma.
So, the i_mmap tree can have the vma which don't include the page if the one is anon page in a file-backed.
This problem is caused by that. Is it enough ?
> > So, I don't reach to your conclusion yet. please teach me.
-- Kinds Regards MinChan Kim
| |