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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: <20200218171052.lwd56nr332qjgs5j@box> References: <20200212041845.25879-1-willy@infradead.org> <20200212041845.25879-14-willy@infradead.org> <20200214135248.zqcqx3erb4pnlvmu@box> <20200214160342.GA7778@bombadil.infradead.org> <20200218141634.zhhjgtv44ux23l3l@box> <20200218161349.GS7778@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200218161349.GS7778@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 Tue, Feb 18, 2020 at 08:13:49AM -0800, Matthew Wilcox wrote: > On Tue, Feb 18, 2020 at 05:16:34PM +0300, Kirill A. Shutemov wrote: > > > + 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. > > after or zero. Yes, I should add a BUG_ON to check for that. > > > Otherwise, looks good. > > Here's what I currently have (I'll add the BUG_ON later): > > commit 7fabe16755365cdc6e80343ef994843ecebde60a > Author: Matthew Wilcox (Oracle) > Date: Sat Feb 1 03:38:49 2020 -0500 > > fs: Support THPs in zero_user_segments > > We can only kmap() one subpage of a THP at a time, so loop over all > relevant subpages, skipping ones which don't need to be zeroed. This is > too large to inline when THPs are enabled and we actually need highmem, > so put it in highmem.c. > > Signed-off-by: Matthew Wilcox (Oracle) Acked-by: Kirill A. Shutemov > > diff --git a/include/linux/highmem.h b/include/linux/highmem.h > index ea5cdbd8c2c3..74614903619d 100644 > --- a/include/linux/highmem.h > +++ b/include/linux/highmem.h > @@ -215,13 +215,18 @@ static inline void clear_highpage(struct page *page) > kunmap_atomic(kaddr); > } > > +#if defined(CONFIG_HIGHMEM) && defined(CONFIG_TRANSPARENT_HUGEPAGE) > +void zero_user_segments(struct page *page, unsigned start1, unsigned end1, > + unsigned start2, unsigned end2); > +#else /* !HIGHMEM || !TRANSPARENT_HUGEPAGE */ This is a neat trick. I like it. Although, it means non-inlined version will never get tested :/ > static inline void zero_user_segments(struct page *page, > - unsigned start1, unsigned end1, > - unsigned start2, unsigned end2) > + unsigned start1, unsigned end1, > + unsigned start2, unsigned end2) > { > + unsigned long i; > void *kaddr = kmap_atomic(page); > > - BUG_ON(end1 > PAGE_SIZE || end2 > PAGE_SIZE); > + BUG_ON(end1 > thp_size(page) || end2 > thp_size(page)); > > if (end1 > start1) > memset(kaddr + start1, 0, end1 - start1); > @@ -230,8 +235,10 @@ static inline void zero_user_segments(struct page *page, > memset(kaddr + start2, 0, end2 - start2); > > kunmap_atomic(kaddr); > - flush_dcache_page(page); > + for (i = 0; i < hpage_nr_pages(page); i++) > + flush_dcache_page(page + i); > } > +#endif /* !HIGHMEM || !TRANSPARENT_HUGEPAGE */ > > static inline void zero_user_segment(struct page *page, > unsigned start, unsigned end) > diff --git a/mm/highmem.c b/mm/highmem.c > index 64d8dea47dd1..3a85c66ef532 100644 > --- a/mm/highmem.c > +++ b/mm/highmem.c > @@ -367,9 +367,67 @@ void kunmap_high(struct page *page) > if (need_wakeup) > wake_up(pkmap_map_wait); > } > - > EXPORT_SYMBOL(kunmap_high); > -#endif > + > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE > +void zero_user_segments(struct page *page, unsigned start1, unsigned end1, > + unsigned start2, unsigned end2) > +{ > + 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; > + } > + 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); > +} > +EXPORT_SYMBOL(zero_user_segments); > +#endif /* CONFIG_TRANSPARENT_HUGEPAGE */ > +#endif /* CONFIG_HIGHMEM */ > > #if defined(HASHED_PAGE_VIRTUAL) > > > > > > > + 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 -- Kirill A. Shutemov