From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3195CC433E3 for ; Fri, 21 Aug 2020 18:06:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 17D7420720 for ; Fri, 21 Aug 2020 18:06:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726884AbgHUSGf (ORCPT ); Fri, 21 Aug 2020 14:06:35 -0400 Received: from mx2.suse.de ([195.135.220.15]:37500 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726057AbgHUSGc (ORCPT ); Fri, 21 Aug 2020 14:06:32 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 31E40AD3A; Fri, 21 Aug 2020 18:06:58 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 170D31E1312; Fri, 21 Aug 2020 20:06:29 +0200 (CEST) Date: Fri, 21 Aug 2020 20:06:29 +0200 From: Jan Kara To: Matthew Wilcox Cc: Jan Kara , linux-mm@kvack.org, Andrew Morton , Hugh Dickins , William Kucharski , Johannes Weiner , linux-kernel@vger.kernel.org Subject: Re: [PATCH 3/7] mm: Add an 'end' parameter to find_get_entries Message-ID: <20200821180629.GF3432@quack2.suse.cz> References: <20200819150555.31669-1-willy@infradead.org> <20200819150555.31669-4-willy@infradead.org> <20200821160759.GE3432@quack2.suse.cz> <20200821163306.GW17456@casper.infradead.org> MIME-Version: 1.0 Content-Type: multipart/mixed; boundary="envbJBWh7q8WU6mo" Content-Disposition: inline In-Reply-To: <20200821163306.GW17456@casper.infradead.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --envbJBWh7q8WU6mo Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Fri 21-08-20 17:33:06, Matthew Wilcox wrote: > On Fri, Aug 21, 2020 at 06:07:59PM +0200, Jan Kara wrote: > > On Wed 19-08-20 16:05:51, Matthew Wilcox (Oracle) wrote: > > > This simplifies the callers and leads to a more efficient implementation > > > since the XArray has this functionality already. > > > > > > Signed-off-by: Matthew Wilcox (Oracle) > > > > The patch looks good to me. Just I'd note that you could drop some: > > > > if (index >= end) > > break; > > > > checks in shmem_undo_range() as well. > > Oh yes, missed a couple ;-) Thanks, I'll add. > > > In the past I was considering moving find_get_entries() to the same API as > > find_get_pages_range() has (which is essentially what you do now, but I > > also had 'start' to be a pgoff_t * so that we can return there where the > > iteration ended in the range). But in the end I've decided the churn is not > > worth the few removed lines and didn't push the patch in the end. What you > > did in this patch seems to be a reasonable middle-ground :) > > I did look at that, but since we're returning the indices, we don't _need_ > to update the index here. > > I have some other ideas for this family of interfaces, but I'm trying > to get the THP work off my plate before getting distracted by that ;-) I have one thing which I wanted to do for a long time but never got to it. IMHO the pagevec abstraction makes the loops unnecessarily complex. I'd rather have helpers like: for_each_mapping_page(mapping, page, start, end) or for_each_mapping_entry(mapping, entry, index, start, end) and hide all the pagevec magic inside those. And it's even not that hard to do including the handling of premature exit from the loop - sample userspace code is attached... Honza -- Jan Kara SUSE Labs, CR --envbJBWh7q8WU6mo Content-Type: text/x-c; charset=us-ascii Content-Disposition: attachment; filename="pvec_looping.c" #include #define PAGEVEC_SIZE 15 struct pagevec { unsigned char nr; int vals[PAGEVEC_SIZE]; }; struct pagevec_iter { unsigned char idx; int last_index; struct pagevec pvec; }; void pagevec_release(struct pagevec *pvec) { int i; for (i = 0; i < pvec->nr; i++) printf("Freeing val %d\n", pvec->vals[i]); pvec->nr = 0; } int pagevec_lookup(struct pagevec *pvec, void *mapping, int *start, int end) { int i; for (i = 0; i < PAGEVEC_SIZE && *start < 29; i++) { pvec->vals[pvec->nr++] = 100 + *start; (*start)++; } return pvec->nr; } static inline int get_next_pvec_val(struct pagevec_iter *pvec_i, void *mapping, int end) { if (pvec_i->idx >= pvec_i->pvec.nr) { pagevec_release(&pvec_i->pvec); if (!pagevec_lookup(&pvec_i->pvec, mapping, &pvec_i->last_index, end)) return 0; pvec_i->idx = 0; } return pvec_i->pvec.vals[pvec_i->idx++]; } void pagevec_release_iter(struct pagevec_iter *pvec_i) { pagevec_release(&pvec_i->pvec); } #define for_each_page(mapping, page, start, end) \ for (struct pagevec_iter pvec_i \ __attribute__ ((cleanup (pagevec_release_iter))) = { \ .idx = 0, .last_index = start, .pvec = { .nr = 0 } }; \ (page = get_next_pvec_val(&pvec_i, mapping, end));) int main(void) { int page; for_each_page(NULL, page, 5, 32) { printf("Seeing val %d\n", page); if (page > 122) break; } return 0; } --envbJBWh7q8WU6mo--