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Shutemov" To: Qian Cai Cc: Matthew Wilcox , Huang Ying , linux-mm@kvack.org Subject: Re: page cache: Store only head pages in i_pages Message-ID: <20190404134553.vuvhgmghlkiw2hgl@kshutemo-mobl1> References: <20190324030422.GE10344@bombadil.infradead.org> <20190329195941.GW10344@bombadil.infradead.org> <1553894734.26196.30.camel@lca.pw> <20190330030431.GX10344@bombadil.infradead.org> <20190330141052.GZ10344@bombadil.infradead.org> <20190331032326.GA10344@bombadil.infradead.org> <20190401091858.s7clitbvf46nomjm@kshutemo-mobl1> <20190401092716.mxw32y4sl66ywc2o@kshutemo-mobl1> <1554383410.26196.39.camel@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1554383410.26196.39.camel@lca.pw> 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 Thu, Apr 04, 2019 at 09:10:10AM -0400, Qian Cai wrote: > On Mon, 2019-04-01 at 12:27 +0300, Kirill A. Shutemov wrote: > > What about patch like this? (completely untested) > > > > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h > > index f939e004c5d1..e3b9bf843dcb 100644 > > --- a/include/linux/pagemap.h > > +++ b/include/linux/pagemap.h > > @@ -335,12 +335,12 @@ static inline struct page *grab_cache_page_nowait(struct > > address_space *mapping, > >   > >  static inline struct page *find_subpage(struct page *page, pgoff_t offset) > >  { > > - unsigned long index = page_index(page); > > + unsigned long mask; > >   > >   VM_BUG_ON_PAGE(PageTail(page), page); > > - VM_BUG_ON_PAGE(index > offset, page); > > - VM_BUG_ON_PAGE(index + (1 << compound_order(page)) <= offset, page); > > - return page - index + offset; > > + > > + mask = (1UL << compound_order(page)) - 1; > > + return page + (offset & mask); > >  } > >   > >  struct page *find_get_entry(struct address_space *mapping, pgoff_t offset); > > No, this then leads to a panic below by LTP hugemmap05. Still reverting the > whole "mm: page cache: store only head pages in i_pages" commit fixed the > problem. Ughh... hugetlb stores pages in page cache differently. What about this: diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h index f939e004c5d1..2e8438a1216a 100644 --- a/include/linux/pagemap.h +++ b/include/linux/pagemap.h @@ -335,12 +335,15 @@ static inline struct page *grab_cache_page_nowait(struct address_space *mapping, static inline struct page *find_subpage(struct page *page, pgoff_t offset) { - unsigned long index = page_index(page); + unsigned long mask; + + if (PageHuge(page)) + return page; VM_BUG_ON_PAGE(PageTail(page), page); - VM_BUG_ON_PAGE(index > offset, page); - VM_BUG_ON_PAGE(index + (1 << compound_order(page)) <= offset, page); - return page - index + offset; + + mask = (1UL << compound_order(page)) - 1; + return page + (offset & mask); } struct page *find_get_entry(struct address_space *mapping, pgoff_t offset); -- Kirill A. Shutemov