Messages in this thread | | | Date | Thu, 17 Sep 2009 00:21:42 +1200 | Subject | Re: [PATCH 2/3] Helper which returns the huge page at a given address (Take 3) | From | Alexey Korolev <> |
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On Wed, Sep 16, 2009 at 12:26 AM, Mel Gorman <mel@csn.ul.ie> wrote: > On Mon, Sep 14, 2009 at 05:18:53PM +1200, Alexey Korolev wrote: >> This patch provides helper function which returns the huge page at a >> given address for population before the page has been faulted. >> It is possible to call hugetlb_get_user_page function in file mmap >> procedure to get pages before they have been requested by user level. >> > > Worth spelling out that this is similar in principal to get_user_pages() > but not as painful to use in this specific context. >
Right. I'll do this. Seems it is important to clearly mention that this function do not introduce new functionality.
>> include/linux/hugetlb.h | 3 +++ >> mm/hugetlb.c | 23 +++++++++++++++++++++++ >> 2 files changed, 26 insertions(+) >> >> --- >> Signed-off-by: Alexey Korolev <akorolev@infradead.org> > > Patch formatting nit. > > diffstat goes below the --- and signed-off-bys go above it. > Right. To be fixed.
>> >> +/* >> + * hugetlb_get_user_page returns the page at a given address for population >> + * before the page has been faulted. >> + */ >> +struct page *hugetlb_get_user_page(struct vm_area_struct *vma, >> + unsigned long address) >> +{ > > Your leader and comments say that the function can be used before the pages > have been faulted. It would presumably require that this function be called > from within a mmap() handler. > > What is happening because you call follow_hugetlb_page() is that the pages > get faulted as part of your mmap() operation. This might make the overall > operation more expensive than you expected. I don't know if what you really > intended was to allocate the huge page, insert it into the page cache and > have it faulted later if the process actually references the page. > > Similarly the leader and comments imply that you expect this to be > called as part of the mmap() operation. However, nothing would appear to > prevent the driver calling this function once the page is already > faulted. Is this intentional?
The implication was not intende. You are correct, the function can be called later. The leader and comment can be rewritten to make this clear.
>> + int ret; >> + int cnt = 1; >> + struct page *pg; >> + struct hstate *h = hstate_vma(vma); >> + >> + address = address & huge_page_mask(h); >> + ret = follow_hugetlb_page(vma->vm_mm, vma, &pg, >> + NULL, &address, &cnt, 0, 0); >> + if (ret < 0) >> + return ERR_PTR(ret); >> + put_page(pg); >> + >> + return pg; >> +} > > I think the caller should be responsible for calling put_page(). Otherwise > there is an outside chance that the page would disappear from you unexpectedly > depending on exactly how the driver was implemented. It would also > behave slightly more like get_user_pages(). > Correct. Lets have behaviour similar to get_user_pages in order to prevent misunderstanding. Put_page will be removed.
Thank you very much for review. Now I am about to clear out the mistakes and will pay a lot more attention to patch descriptions and comments.
Thanks, Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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