From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with SMTP id DA4BF6B004D for ; Tue, 18 Aug 2009 23:29:29 -0400 (EDT) Received: by an-out-0708.google.com with SMTP id c3so1624065ana.26 for ; Tue, 18 Aug 2009 20:29:27 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20090818082247.GA31469@csn.ul.ie> References: <20090818082247.GA31469@csn.ul.ie> Date: Wed, 19 Aug 2009 15:29:27 +1200 Message-ID: <202cde0e0908182029k73292ee9k6d2782b40beaaa1c@mail.gmail.com> Subject: Re: [PATCH 1/3]HTLB mapping for drivers. Alloc functions & some export symbols(take 2) From: Alexey Korolev Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: Mel Gorman Cc: Alexey Korolev , linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: Hi, >> =C2=A0 * Use a helper variable to find the next node and then >> =C2=A0 * copy it back to hugetlb_next_nid afterwards: >> =C2=A0 * 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=3Dlinux-mm&m=3D125025895815115&w=3D2 > > ? 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 =3D current->mm->get_unmapped_area; if (file && file->f_op && file->f_op->get_unmapped_area) get_area =3D 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 =3D hugetlb_get_unmapped_area; addr =3D 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 =3D file; get_file(file); error =3D 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 =3Dhugetlbfs_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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org