Messages in this thread Patch in this message | | | Subject | [patch 37/39] remap_file_pages protection support: wrong "historical" code for review - 1 | From | blaisorblade@yahoo ... | Date | Fri, 12 Aug 2005 20:36:34 +0200 |
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From: Ingo Molnar <mingo@elte.hu>, Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it>
This "fast-path" was contained in the original remap-file-pages-prot-2.6.4-rc1-mm1-A1.patch from Ingo Molnar*; I think this code is wrong, but I'm sending it for review anyway, because I'm unsure (and in fact, in the end I found the reason for this).
What I think is that this patch (done only for filemap_populate, not for shmem_populate) calls zap_page_range() when installing mappings with PROT_NONE protection. The purpose is to avoid an useless page lookup; but the PTE's will be simply marked as absent, not as _PAGE_NONE. So, with this fastpath, pages would be remapped again in their "default" position.
In this case, probably a possible fix is to add yet another param in "zap_details" to mark all PTE's as PROT_NONE ones. Using details->nonlinear_vma has the inconvenient of using details->{first,last}_index and of leaving file entries unchanged.
* available at http://www.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.5/2.6.5-mm1/dropped/remap-file-pages-prot-2.6.4-rc1-mm1-A1.patch
Signed-off-by: Paolo 'Blaisorblade' Giarrusso <blaisorblade@yahoo.it> ---
linux-2.6.git-paolo/mm/filemap.c | 9 +++++++++ 1 files changed, 9 insertions(+)
diff -puN mm/filemap.c~rfp-wrong2 mm/filemap.c --- linux-2.6.git/mm/filemap.c~rfp-wrong2 2005-08-12 18:31:32.000000000 +0200 +++ linux-2.6.git-paolo/mm/filemap.c 2005-08-12 18:31:32.000000000 +0200 @@ -1495,6 +1495,15 @@ int filemap_populate(struct vm_area_stru struct page *page; int err; + /* + * mapping-removal fastpath: + */ + if ((vma->vm_flags & VM_SHARED) && + (pgprot_val(prot) == pgprot_val(PAGE_NONE))) { + zap_page_range(vma, addr, len, NULL); + return 0; + } + if (!nonblock) force_page_cache_readahead(mapping, vma->vm_file, pgoff, len >> PAGE_CACHE_SHIFT); _ - 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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