From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with SMTP id 05E666B003D for ; Fri, 8 May 2009 04:09:48 -0400 (EDT) Date: Fri, 8 May 2009 16:09:21 +0800 From: Wu Fengguang Subject: Re: [PATCH -mm] vmscan: make mapped executable pages the first class citizen Message-ID: <20090508080921.GA25411@localhost> References: <20090430215034.4748e615@riellaptop.surriel.com> <20090430195439.e02edc26.akpm@linux-foundation.org> <49FB01C1.6050204@redhat.com> <20090501123541.7983a8ae.akpm@linux-foundation.org> <20090503031539.GC5702@localhost> <1241432635.7620.4732.camel@twins> <20090507121101.GB20934@localhost> <20090507151039.GA2413@cmpxchg.org> <20090508030209.GA8892@localhost> <20090508163042.ba4ef116.minchan.kim@barrios-desktop> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090508163042.ba4ef116.minchan.kim@barrios-desktop> Sender: owner-linux-mm@kvack.org To: Minchan Kim Cc: Johannes Weiner , Andrew Morton , Peter Zijlstra , Rik van Riel , "linux-kernel@vger.kernel.org" , "tytso@mit.edu" , "linux-mm@kvack.org" , Elladan , Nick Piggin , Christoph Lameter , KOSAKI Motohiro List-ID: On Fri, May 08, 2009 at 03:30:42PM +0800, Minchan Kim wrote: > Hi, Let me have a question. > > On Fri, 8 May 2009 11:02:09 +0800 > Wu Fengguang wrote: > > > On Thu, May 07, 2009 at 11:10:39PM +0800, Johannes Weiner wrote: > > > On Thu, May 07, 2009 at 08:11:01PM +0800, Wu Fengguang wrote: > > > > Introduce AS_EXEC to mark executables and their linked libraries, and to > > > > protect their referenced active pages from being deactivated. > > > > > > > > CC: Elladan > > > > CC: Nick Piggin > > > > CC: Johannes Weiner > > > > CC: Christoph Lameter > > > > CC: KOSAKI Motohiro > > > > Acked-by: Peter Zijlstra > > > > Acked-by: Rik van Riel > > > > Signed-off-by: Wu Fengguang > > > > --- > > > > include/linux/pagemap.h | 1 + > > > > mm/mmap.c | 2 ++ > > > > mm/nommu.c | 2 ++ > > > > mm/vmscan.c | 35 +++++++++++++++++++++++++++++++++-- > > > > 4 files changed, 38 insertions(+), 2 deletions(-) > > > > > > > > --- linux.orig/include/linux/pagemap.h > > > > +++ linux/include/linux/pagemap.h > > > > @@ -25,6 +25,7 @@ enum mapping_flags { > > > > #ifdef CONFIG_UNEVICTABLE_LRU > > > > AS_UNEVICTABLE = __GFP_BITS_SHIFT + 3, /* e.g., ramdisk, SHM_LOCK */ > > > > #endif > > > > + AS_EXEC = __GFP_BITS_SHIFT + 4, /* mapped PROT_EXEC somewhere */ > > > > }; > > > > > > > > static inline void mapping_set_error(struct address_space *mapping, int error) > > > > --- linux.orig/mm/mmap.c > > > > +++ linux/mm/mmap.c > > > > @@ -1194,6 +1194,8 @@ munmap_back: > > > > goto unmap_and_free_vma; > > > > if (vm_flags & VM_EXECUTABLE) > > > > added_exe_file_vma(mm); > > > > + if (vm_flags & VM_EXEC) > > > > + set_bit(AS_EXEC, &file->f_mapping->flags); > > > > } else if (vm_flags & VM_SHARED) { > > > > error = shmem_zero_setup(vma); > > > > if (error) > > > > --- linux.orig/mm/nommu.c > > > > +++ linux/mm/nommu.c > > > > @@ -1224,6 +1224,8 @@ unsigned long do_mmap_pgoff(struct file > > > > added_exe_file_vma(current->mm); > > > > vma->vm_mm = current->mm; > > > > } > > > > + if (vm_flags & VM_EXEC) > > > > + set_bit(AS_EXEC, &file->f_mapping->flags); > > > > } > > > > > > I find it a bit ugly that it applies an attribute of the memory area > > > (per mm) to the page cache mapping (shared). Because this in turn > > > means that the reference through a non-executable vma might get the > > > pages rotated just because there is/was an executable mmap around. > > > > Right, the intention was to identify a whole executable/library file, > > eg. /bin/bash or /lib/libc-2.9.so, covering both _text_ and _data_ > > sections. > > But, your patch is care just text section. > Do I miss something ? This patch actually protects the mapped pages in the whole executable file. Sorry, the title was a bit misleading.. > > > > down_write(&nommu_region_sem); > > > > --- linux.orig/mm/vmscan.c > > > > +++ linux/mm/vmscan.c > > > > @@ -1230,6 +1230,7 @@ static void shrink_active_list(unsigned > > > > unsigned long pgmoved; > > > > unsigned long pgscanned; > > > > LIST_HEAD(l_hold); /* The pages which were snipped off */ > > > > + LIST_HEAD(l_active); > > > > LIST_HEAD(l_inactive); > > > > struct page *page; > > > > struct pagevec pvec; > > > > @@ -1269,8 +1270,15 @@ static void shrink_active_list(unsigned > > > > > > > > /* page_referenced clears PageReferenced */ > > > > if (page_mapping_inuse(page) && > > > > - page_referenced(page, 0, sc->mem_cgroup)) > > > > + page_referenced(page, 0, sc->mem_cgroup)) { > > > > + struct address_space *mapping = page_mapping(page); > > > > + > > > > pgmoved++; > > > > + if (mapping && test_bit(AS_EXEC, &mapping->flags)) { > > > > + list_add(&page->lru, &l_active); > > > > + continue; > > > > + } > > > > + } > > > > > > Since we walk the VMAs in page_referenced anyway, wouldn't it be > > > better to check if one of them is executable? This would even work > > > for executable anon pages. After all, there are applications that cow > > > executable mappings (sbcl and other language environments that use an > > > executable, run-time modified core image come to mind). > > > > The page_referenced() path will only cover the _text_ section. But > > Why did you said that "The page_referenced() path will only cover the ""_text_"" section" ? > Could you elaborate please ? I was under the wild assumption that only the _text_ section will be PROT_EXEC mapped. No? Thanks, Fengguang > > yeah, the _data_ section is more likely to grow huge in some rare cases. > > > > Thanks, > > Fengguang > > > > -- > > 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 > > > -- > Kinds Regards > Minchan Kim -- 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