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Shutemov" To: Song Liu Cc: "linux-mm@kvack.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "matthew.wilcox@oracle.com" , "kirill.shutemov@linux.intel.com" , Kernel Team , "william.kucharski@oracle.com" , "akpm@linux-foundation.org" , "hdanton@sina.com" Subject: Re: [PATCH v7 5/6] mm,thp: add read-only THP support for (non-shmem) FS Message-ID: <20190624151528.fnz3hvlnyvea3ytn@box> References: <20190623054749.4016638-1-songliubraving@fb.com> <20190623054749.4016638-6-songliubraving@fb.com> <20190624124746.7evd2hmbn3qg3tfs@box> <52BDA50B-7CBF-4333-9D15-0C17FD04F6ED@fb.com> <20190624142747.chy5s3nendxktm3l@box> <20190624145453.u4ej3e4ktyyqjite@box> <5BE23F34-B611-496B-9277-A09C9CC784B1@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <5BE23F34-B611-496B-9277-A09C9CC784B1@fb.com> User-Agent: NeoMutt/20180716 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon, Jun 24, 2019 at 03:04:21PM +0000, Song Liu wrote: > > > > On Jun 24, 2019, at 7:54 AM, Kirill A. Shutemov wrote: > > > > On Mon, Jun 24, 2019 at 02:42:13PM +0000, Song Liu wrote: > >> > >> > >>> On Jun 24, 2019, at 7:27 AM, Kirill A. Shutemov wrote: > >>> > >>> On Mon, Jun 24, 2019 at 02:01:05PM +0000, Song Liu wrote: > >>>>>> @@ -1392,6 +1403,23 @@ static void collapse_file(struct mm_struct *mm, > >>>>>> result = SCAN_FAIL; > >>>>>> goto xa_unlocked; > >>>>>> } > >>>>>> + } else if (!page || xa_is_value(page)) { > >>>>>> + xas_unlock_irq(&xas); > >>>>>> + page_cache_sync_readahead(mapping, &file->f_ra, file, > >>>>>> + index, PAGE_SIZE); > >>>>>> + lru_add_drain(); > >>>>> > >>>>> Why? > >>>> > >>>> isolate_lru_page() is likely to fail if we don't drain the pagevecs. > >>> > >>> Please add a comment. > >> > >> Will do. > >> > >>> > >>>>>> + page = find_lock_page(mapping, index); > >>>>>> + if (unlikely(page == NULL)) { > >>>>>> + result = SCAN_FAIL; > >>>>>> + goto xa_unlocked; > >>>>>> + } > >>>>>> + } else if (!PageUptodate(page)) { > >>>>> > >>>>> Maybe we should try wait_on_page_locked() here before give up? > >>>> > >>>> Are you referring to the "if (!PageUptodate(page))" case? > >>> > >>> Yes. > >> > >> I think this case happens when another thread is reading the page in. > >> I could not think of a way to trigger this condition for testing. > >> > >> On the other hand, with current logic, we will retry the page on the > >> next scan, so I guess this is OK. > > > > What I meant that calling wait_on_page_locked() on !PageUptodate() page > > will likely make it up-to-date and we don't need to SCAN_FAIL the attempt. > > > > Yeah, I got the point. My only concern is that I don't know how to > reliably trigger this case for testing. I can try to trigger it. But I > don't know whether it will happen easily. Atrifically slowing down IO should do the trick. -- Kirill A. Shutemov