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Shutemov" To: Matthew Wilcox Cc: linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 13/25] fs: Add zero_user_large Message-ID: <20200218141634.zhhjgtv44ux23l3l@box> References: <20200212041845.25879-1-willy@infradead.org> <20200212041845.25879-14-willy@infradead.org> <20200214135248.zqcqx3erb4pnlvmu@box> <20200214160342.GA7778@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200214160342.GA7778@bombadil.infradead.org> 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 Fri, Feb 14, 2020 at 08:03:42AM -0800, Matthew Wilcox wrote: > On Fri, Feb 14, 2020 at 04:52:48PM +0300, Kirill A. Shutemov wrote: > > On Tue, Feb 11, 2020 at 08:18:33PM -0800, Matthew Wilcox wrote: > > > From: "Matthew Wilcox (Oracle)" > > > > > > We can't kmap() a THP, so add a wrapper around zero_user() for large > > > pages. > > > > I would rather address it closer to the root: make zero_user_segments() > > handle compound pages. > > Hah. I ended up doing that, but hadn't sent it out. I don't like > how ugly it is: > > @@ -219,18 +219,57 @@ static inline void zero_user_segments(struct page *page, > unsigned start1, unsigned end1, > unsigned start2, unsigned end2) > { > - void *kaddr = kmap_atomic(page); > - > - BUG_ON(end1 > PAGE_SIZE || end2 > PAGE_SIZE); > - > - if (end1 > start1) > - memset(kaddr + start1, 0, end1 - start1); > - > - if (end2 > start2) > - memset(kaddr + start2, 0, end2 - start2); > - > - kunmap_atomic(kaddr); > - flush_dcache_page(page); > + unsigned int i; > + > + BUG_ON(end1 > thp_size(page) || end2 > thp_size(page)); > + > + for (i = 0; i < hpage_nr_pages(page); i++) { > + void *kaddr; > + unsigned this_end; > + > + if (end1 == 0 && start2 >= PAGE_SIZE) { > + start2 -= PAGE_SIZE; > + end2 -= PAGE_SIZE; > + continue; > + } > + > + if (start1 >= PAGE_SIZE) { > + start1 -= PAGE_SIZE; > + end1 -= PAGE_SIZE; > + if (start2) { > + start2 -= PAGE_SIZE; > + end2 -= PAGE_SIZE; > + } You assume start2/end2 is always after start1/end1 in the page. Is it always true? If so, I would add BUG_ON() for it. Otherwise, looks good. > + continue; > + } > + > + kaddr = kmap_atomic(page + i); > + > + this_end = min_t(unsigned, end1, PAGE_SIZE); > + if (end1 > start1) > + memset(kaddr + start1, 0, this_end - start1); > + end1 -= this_end; > + start1 = 0; > + > + if (start2 >= PAGE_SIZE) { > + start2 -= PAGE_SIZE; > + end2 -= PAGE_SIZE; > + } else { > + this_end = min_t(unsigned, end2, PAGE_SIZE); > + if (end2 > start2) > + memset(kaddr + start2, 0, this_end - start2); > + end2 -= this_end; > + start2 = 0; > + } > + > + kunmap_atomic(kaddr); > + flush_dcache_page(page + i); > + > + if (!end1 && !end2) > + break; > + } > + > + BUG_ON((start1 | start2 | end1 | end2) != 0); > } > > I think at this point it has to move out-of-line too. > > > > +static inline void zero_user_large(struct page *page, > > > + unsigned start, unsigned size) > > > +{ > > > + unsigned int i; > > > + > > > + for (i = 0; i < thp_order(page); i++) { > > > + if (start > PAGE_SIZE) { > > > > Off-by-one? >= ? > > Good catch; I'd also noticed that when I came to redo the zero_user_segments(). > -- Kirill A. Shutemov