Messages in this thread | | | Date | Sat, 22 Feb 2014 11:44:24 -0600 | From | Jay Cornwall <> | Subject | Re: put page on transparent huge page leaks ? |
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On 2014-02-21 20:31, Kirill A. Shutemov wrote: > On Fri, Feb 21, 2014 at 11:23:39AM -0600, Jay Cornwall wrote: >> I'm tracking a possible memory leak in iommu/amd. The driver uses this >> logic >> to fault a page in response to a PRI from a device: >> >> npages = get_user_pages(fault->state->task, fault->state->mm, >> fault->address, 1, write, 0, &page, NULL); >> >> if (npages == 1) >> put_page(page); >> else >> ... >> >> This works correctly when get_user_pages returns a 4KB page. When >> transparent huge pages are enabled any 2MB page returned by this call >> appears to leak on process exit. The non-cached memory usage stays >> elevated >> by the set of faulted 2MB pages. This behavior is not observed when >> the >> exception handler demand faults 2MB pages. > > Could you show output of dump_page() on 2M pages for both points?
get_user_pages(): page:ffffea000ffa00c0 count:0 mapcount:1 mapping: (null) index:0x0 page flags: 0x2fffe0000008000(tail) // page_count(page)=3 (head page) put_page(): page:ffffea000ffa00c0 count:0 mapcount:0 mapping: (null) index:0x0 page flags: 0x2fffe0000008000(tail) // page_count(page)=3 (head page)
Repeat on the same page.
get_user_pages(): page:ffffea000ffa00c0 count:0 mapcount:1 mapping: (null) index:0x0 page flags: 0x2fffe0000008000(tail) // page_count(page)=4 (head page) put_page(): page:ffffea000ffa00c0 count:0 mapcount:0 mapping: (null) index:0x0 page flags: 0x2fffe0000008000(tail) // page_count(page)=4 (head page)
The head page appears to be leaking a reference. There is *no leak* if the driver faults the head page directly.
> My guess is that your page is PageTail(). Refcounting for tail pages is > different: on get_page() we increase *->_mapcount* of tail and increase > ->_count of relevant head page. ->_count of tail pages should always be > zero, but it's 3 in your case which is odd.
That's correct, this is a tail page. page_count() references the head page:
static inline int page_count(struct page *page) { return atomic_read(&compound_head(page)->_count); }
> BTW, I don't see where you take mmap_sem in > drivers/iommu/amd_iommu_v2.c, > which is required for gup. Do I miss something?
You're right. I have a patch applied on my local branch to fix this.
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