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Date: Wed, 19 Aug 2009 15:29:27 +1200 From: Alexey Korolev <akorolex@...il.com> To: Mel Gorman <mel@....ul.ie> Cc: Alexey Korolev <akorolev@...radead.org>, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/3]HTLB mapping for drivers. Alloc functions & some export symbols(take 2) Hi, >> * Use a helper variable to find the next node and then >> * copy it back to hugetlb_next_nid afterwards: >> * otherwise there's a window in which a racer might > > I haven't read through the whole patchset properly yet, but at this > point it's looking like you are going to expect drivers to create a file > and then manually populate the page cache with hugepages they allocate > directly from here. That would appear to put a large burden of VM > knowledge upon a device driver author. The patch would also appear to > expose a lot of hugetlbfs internals. > > Have you looked at Eric Munson's patches on the implementation of > MAP_HUGETLB in the patch set > > http://marc.info/?l=linux-mm&m=125025895815115&w=2 > > ? Right. Simplicity is very important here and I just haven't find a good way to make it simpler yet. Thanks for the link neat approach is a thing I really need now. I've studied the code and it has quite nice approach which could be helpful. > > In that patchset, it was a very small number of changes required to > expose a mapping private or shared to userspace. > > Would it make more sense to take an approach like that and instead add > an additional helper within hugetlbfs (instead of the driver) that would > return a pinned page at a given offset within a hugetlbfs file? > I believe it possible to to have a helper. The main problem here is this: we need to have a file which provides hugetlb mapping and which is not a part of Hugetlbfs. So the file does not have hugetlbfs file operations.It means it is necessary to call somehow hugetlb_get_unmapped_area & hugetlbfs_file_mmap for the file on hugetlbfs associated with the file related to device. Probably, if we have non-hugetlbfs file and want to have huge pages mappings it could make sense to have this approach: add the following lines to mmap.c/get_unmapped_area function: get_area = current->mm->get_unmapped_area; if (file && file->f_op && file->f_op->get_unmapped_area) get_area = file->f_op->get_unmapped_area; + /* Call hugetlb_get_unmapped_area If non hugetlbfs file has huge page mapping */ + if (file && mapping_hugetlb(file->f_mapping) && !is_file_hugepages(file)) + get_area = hugetlb_get_unmapped_area; addr = get_area(file, addr, len, pgoff, flags); if (IS_ERR_VALUE(addr)) return addr; add the following lines to mmap.c/mmap_region function: } vma->vm_file = file; get_file(file); error = file->f_op->mmap(file, vma); if (error) goto unmap_and_free_vma; + /* + * If non non hugetlbfs file has huge page mapping mmap must be called twice + * first time for proceeding file->fops->mmap second time we must call hugetlbfs mmap + */ + if (mapping_hugetlb(file->f_mapping) && !is_file_hugepages(file)) + error =hugetlbfs_file_mmap(file, vma); + if (error) + goto unmap_and_free_vma; if (vm_flags & VM_EXECUTABLE) Where mapping_hugetlb is +static inline int mapping_hugetlb(struct address_space *mapping) +{ + if (likely(mapping)) + return test_bit(AS_HUGETLB, &mapping->flags); + return 0; +} + In addition we also need to introduce hugetlbfs_sb_info getting macro to avoid issues in hugetlb_get_quota/hugetlb_put_quota functions. In this case a driver just need to announce that file has huge page mapping (mapping_set_hugetlb(file->f_mapping)), add some pages to page cache and set-up proper VM flag in flie->f_ops->mmap. Do you see anything really important being missed in this approach? Thanks, Alexey -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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