Messages in this thread | | | Date | Wed, 24 Aug 2016 11:30:44 +0100 | From | Catalin Marinas <> | Subject | Re: [PATCH 1/1] arm64/hugetlb: clear PG_dcache_clean if the page is dirty when munmap |
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On Wed, Aug 24, 2016 at 05:00:50PM +0800, Leizhen (ThunderTown) wrote: > > > On 2016/8/24 1:28, Catalin Marinas wrote: > > On Mon, Aug 22, 2016 at 12:19:04PM +0800, Leizhen (ThunderTown) wrote: > >> On 2016/7/20 17:19, Catalin Marinas wrote: > >>> On Wed, Jul 20, 2016 at 10:46:27AM +0800, Leizhen (ThunderTown) wrote: > >>>>>>>> On 2016/7/8 21:54, Catalin Marinas wrote: > >>>>>>>>> ------------8<---------------- > >>>>>>>>> diff --git a/arch/arm64/mm/flush.c b/arch/arm64/mm/flush.c > >>>>>>>>> index dbd12ea8ce68..c753fa804165 100644 > >>>>>>>>> --- a/arch/arm64/mm/flush.c > >>>>>>>>> +++ b/arch/arm64/mm/flush.c > >>>>>>>>> @@ -75,7 +75,8 @@ void __sync_icache_dcache(pte_t pte, unsigned long addr) > >>>>>>>>> if (!page_mapping(page)) > >>>>>>>>> return; > >>>>>>>>> > >>>>>>>>> - if (!test_and_set_bit(PG_dcache_clean, &page->flags)) > >>>>>>>>> + if (!test_and_set_bit(PG_dcache_clean, &page->flags) || > >>>>>>>>> + PageDirty(page)) > >>>>>>>>> sync_icache_aliases(page_address(page), > >>>>>>>>> PAGE_SIZE << compound_order(page)); > >>>>>>>>> else if (icache_is_aivivt()) > >>>>>>>>> ----------------8<--------------------- > >>>> > >>>> Do you plan to send this patch? My colleagues told me that if our > >>>> patches are quite different, it should be Signed-off-by you. > >>> > >>> The reason I'm not sending it is that I don't fully understand how it > >>> solves the problem for a shared file mmap(), not just hugetlbfs. As I > >>> said in an earlier email: after an msync() in user space we > >>> should flush the pages to disk via write_cache_pages(). This function > >> Hi Catalin: > >> I'm so sorry for my fault. The previous small pages test result I actually ran on ramfs. > >> Today, I ran the case on harddisk fs, it worked well without this patch. > >> > >> Summarized as follows: > >> small pages on ramfs: need this patch > >> small pages on harddisk fs: no need this patch > >> hugetlbfs: need this patch > > > > I would add: > > > > small pages over nfs: fails with or without this patch > > > > (tested on Juno, Cortex-A57; seems to be fixed if I remove the > > PG_dcache_clean test altogether but, well, we end up over-flushing) > > > > I assume that when using a hard drive, it goes through the block I/O > > layer and we may have a flush_dcache_page() called when the kernel is > > about to read a page that has been mapped in user space. This would > > clear the PG_dcache_clean bit and subsequent __sync_icache_dcache() > > would perform cache maintenance. > > > > Could you try on your system the test case without the msync() call? I'm > > According to my test results: without msync, the test case may failed.
Thanks. Just to be clear, does the test generate a file on on a hard drive?
> 10-175-112-211:~ # ./tst_small_page_no_msync > Test is Failed: The result is 0x316b9, expect = 0x365a5 > 10-175-112-211:~ # ./tst_small_page_no_msync > Test is Failed: The result is 0x31023, expect = 0x31efa > 10-175-112-211:~ # ./tst_small_page_no_msync > Test is Passed: The result is 0x31efa, expect = 0x31efa > > 10-175-112-211:~ # ./tst_small_page > Test is Passed: The result is 0x31eb7, expect = 0x31eb7 > 10-175-112-211:~ # ./tst_small_page > Test is Passed: The result is 0x3111f, expect = 0x3111f > 10-175-112-211:~ # ./tst_small_page > Test is Passed: The result is 0x3111f, expect = 0x3111f
How many tests did you run for the "passed" case? With NFS it may sometime take minutes before a failure (I use the "watch" command with a slightly modified test to return non-zero in case of value mismatch).
While we indeed see failures on multiple filesystem types, I wonder whether this test case is actually expected to work. If I modify the test to pass O_TRUNC to open(), I can no longer see failures. So any standard tool that copies/creates executable files (gcc, dpkg, cp, rsync etc.) wouldn't encounter such issues since they truncate the original file and old page cache pages would be removed.
Do you have a real use-case where a task mmap's an executable file, modifies it in place and expects another task to see the new instructions without user-space cache maintenance?
-- Catalin
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