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Shutemov" To: Vlastimil Babka Cc: linux-mm@kvack.org, Andrew Morton , linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Michal Hocko , Mel Gorman , Matthew Wilcox Subject: Re: [PATCH v2 2/4] mm, page_owner: record page owner for each subpage Message-ID: <20190924113135.2ekb7bmil3rxge6w@box> References: <20190820131828.22684-1-vbabka@suse.cz> <20190820131828.22684-3-vbabka@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190820131828.22684-3-vbabka@suse.cz> 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 Tue, Aug 20, 2019 at 03:18:26PM +0200, Vlastimil Babka wrote: > Currently, page owner info is only recorded for the first page of a high-order > allocation, and copied to tail pages in the event of a split page. With the > plan to keep previous owner info after freeing the page, it would be benefical > to record page owner for each subpage upon allocation. This increases the > overhead for high orders, but that should be acceptable for a debugging option. > > The order stored for each subpage is the order of the whole allocation. This > makes it possible to calculate the "head" pfn and to recognize "tail" pages > (quoted because not all high-order allocations are compound pages with true > head and tail pages). When reading the page_owner debugfs file, keep skipping > the "tail" pages so that stats gathered by existing scripts don't get inflated. > > Signed-off-by: Vlastimil Babka > --- > mm/page_owner.c | 40 ++++++++++++++++++++++++++++------------ > 1 file changed, 28 insertions(+), 12 deletions(-) > > diff --git a/mm/page_owner.c b/mm/page_owner.c > index addcbb2ae4e4..813fcb70547b 100644 > --- a/mm/page_owner.c > +++ b/mm/page_owner.c > @@ -154,18 +154,23 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags) > return handle; > } > > -static inline void __set_page_owner_handle(struct page_ext *page_ext, > - depot_stack_handle_t handle, unsigned int order, gfp_t gfp_mask) > +static inline void __set_page_owner_handle(struct page *page, > + struct page_ext *page_ext, depot_stack_handle_t handle, > + unsigned int order, gfp_t gfp_mask) > { > struct page_owner *page_owner; > + int i; > > - page_owner = get_page_owner(page_ext); > - page_owner->handle = handle; > - page_owner->order = order; > - page_owner->gfp_mask = gfp_mask; > - page_owner->last_migrate_reason = -1; > + for (i = 0; i < (1 << order); i++) { > + page_owner = get_page_owner(page_ext); > + page_owner->handle = handle; > + page_owner->order = order; > + page_owner->gfp_mask = gfp_mask; > + page_owner->last_migrate_reason = -1; > + __set_bit(PAGE_EXT_OWNER, &page_ext->flags); > > - __set_bit(PAGE_EXT_OWNER, &page_ext->flags); > + page_ext = lookup_page_ext(page + i); Isn't it off-by-one? You are calculating page_ext for the next page, right? And cant we just do page_ext++ here instead? > + } > } > > noinline void __set_page_owner(struct page *page, unsigned int order, > @@ -178,7 +183,7 @@ noinline void __set_page_owner(struct page *page, unsigned int order, > return; > > handle = save_stack(gfp_mask); > - __set_page_owner_handle(page_ext, handle, order, gfp_mask); > + __set_page_owner_handle(page, page_ext, handle, order, gfp_mask); > } > > void __set_page_owner_migrate_reason(struct page *page, int reason) > @@ -204,8 +209,11 @@ void __split_page_owner(struct page *page, unsigned int order) > > page_owner = get_page_owner(page_ext); > page_owner->order = 0; > - for (i = 1; i < (1 << order); i++) > - __copy_page_owner(page, page + i); > + for (i = 1; i < (1 << order); i++) { > + page_ext = lookup_page_ext(page + i); Again, page_ext++? > + page_owner = get_page_owner(page_ext); > + page_owner->order = 0; > + } > } > > void __copy_page_owner(struct page *oldpage, struct page *newpage) > @@ -483,6 +491,13 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos) > > page_owner = get_page_owner(page_ext); > > + /* > + * Don't print "tail" pages of high-order allocations as that > + * would inflate the stats. > + */ > + if (!IS_ALIGNED(pfn, 1 << page_owner->order)) > + continue; > + > /* > * Access to page_ext->handle isn't synchronous so we should > * be careful to access it. > @@ -562,7 +577,8 @@ static void init_pages_in_zone(pg_data_t *pgdat, struct zone *zone) > continue; > > /* Found early allocated page */ > - __set_page_owner_handle(page_ext, early_handle, 0, 0); > + __set_page_owner_handle(page, page_ext, early_handle, > + 0, 0); > count++; > } > cond_resched(); > -- > 2.22.0 > > -- Kirill A. Shutemov