From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl0-f71.google.com (mail-pl0-f71.google.com [209.85.160.71]) by kanga.kvack.org (Postfix) with ESMTP id D08D66B000A for ; Tue, 10 Jul 2018 02:53:39 -0400 (EDT) Received: by mail-pl0-f71.google.com with SMTP id y7-v6so11764403plt.17 for ; Mon, 09 Jul 2018 23:53:39 -0700 (PDT) Received: from mga12.intel.com (mga12.intel.com. [192.55.52.136]) by mx.google.com with ESMTPS id h5-v6si16216514plr.268.2018.07.09.23.53.38 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 09 Jul 2018 23:53:38 -0700 (PDT) From: "Huang\, Ying" Subject: Re: [PATCH -mm -v4 04/21] mm, THP, swap: Support PMD swap mapping in swapcache_free_cluster() References: <20180622035151.6676-1-ying.huang@intel.com> <20180622035151.6676-5-ying.huang@intel.com> Date: Tue, 10 Jul 2018 14:53:35 +0800 In-Reply-To: (Dave Hansen's message of "Mon, 9 Jul 2018 10:11:57 -0700") Message-ID: <874lh7intc.fsf@yhuang-dev.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ascii Sender: owner-linux-mm@kvack.org List-ID: To: Dave Hansen Cc: Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Andrea Arcangeli , Michal Hocko , Johannes Weiner , Shaohua Li , Hugh Dickins , Minchan Kim , Rik van Riel , Naoya Horiguchi , Zi Yan , Daniel Jordan Dave Hansen writes: >> +#ifdef CONFIG_THP_SWAP >> +static inline int cluster_swapcount(struct swap_cluster_info *ci) >> +{ >> + if (!ci || !cluster_is_huge(ci)) >> + return 0; >> + >> + return cluster_count(ci) - SWAPFILE_CLUSTER; >> +} >> +#else >> +#define cluster_swapcount(ci) 0 >> +#endif > > Dumb questions, round 2: On a CONFIG_THP_SWAP=n build, presumably, > cluster_is_huge()=0 always, so cluster_swapout() always returns 0. Right? > > So, why the #ifdef? #ifdef here is to reduce the code size for !CONFIG_THP_SWAP. >> /* >> * It's possible scan_swap_map() uses a free cluster in the middle of free >> * cluster list. Avoiding such abuse to avoid list corruption. >> @@ -905,6 +917,7 @@ static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx) >> struct swap_cluster_info *ci; >> >> ci = lock_cluster(si, offset); >> + memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER); >> cluster_set_count_flag(ci, 0, 0); >> free_cluster(si, idx); >> unlock_cluster(ci); > > This is another case of gloriously comment-free code, but stuff that > _was_ covered in the changelog. I'd much rather have code comments than > changelog comments. Could we fix that? > > I'm generally finding it quite hard to review this because I keep having > to refer back to the changelog to see if what you are doing matches what > you said you were doing. Sure. Will fix this. >> @@ -1288,24 +1301,30 @@ static void swapcache_free_cluster(swp_entry_t entry) >> >> ci = lock_cluster(si, offset); >> VM_BUG_ON(!cluster_is_huge(ci)); >> + VM_BUG_ON(!is_cluster_offset(offset)); >> + VM_BUG_ON(cluster_count(ci) < SWAPFILE_CLUSTER); >> map = si->swap_map + offset; >> - for (i = 0; i < SWAPFILE_CLUSTER; i++) { >> - val = map[i]; >> - VM_BUG_ON(!(val & SWAP_HAS_CACHE)); >> - if (val == SWAP_HAS_CACHE) >> - free_entries++; >> + if (!cluster_swapcount(ci)) { >> + for (i = 0; i < SWAPFILE_CLUSTER; i++) { >> + val = map[i]; >> + VM_BUG_ON(!(val & SWAP_HAS_CACHE)); >> + if (val == SWAP_HAS_CACHE) >> + free_entries++; >> + } >> + if (free_entries != SWAPFILE_CLUSTER) >> + cluster_clear_huge(ci); >> } > > Also, I'll point out that cluster_swapcount() continues the horrific > naming of cluster_couunt(), not saying what the count is *of*. The > return value doesn't help much: > > return cluster_count(ci) - SWAPFILE_CLUSTER; We have page_swapcount() for page, swp_swapcount() for swap entry. cluster_swapcount() tries to mimic them for swap cluster. But I am not good at naming in general. What's your suggestion? Best Regards, Huang, Ying