Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757796AbcC2TXT (ORCPT ); Tue, 29 Mar 2016 15:23:19 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:50295 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753553AbcC2TXP (ORCPT ); Tue, 29 Mar 2016 15:23:15 -0400 Date: Tue, 29 Mar 2016 12:23:13 -0700 From: Andrew Morton To: Vlastimil Babka Cc: js1304@gmail.com, Hugh Dickins , Johannes Berg , "David S. Miller" , Sunil Goutham , Chris Metcalf , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Joonsoo Kim Subject: Re: [PATCH v2 2/2] mm: rename _count, field of the struct page, to _refcount Message-Id: <20160329122313.3c24964faab99f46c960b19b@linux-foundation.org> In-Reply-To: <56FA4A93.6090502@suse.cz> References: <1459146601-11448-1-git-send-email-iamjoonsoo.kim@lge.com> <1459146601-11448-2-git-send-email-iamjoonsoo.kim@lge.com> <56FA4A93.6090502@suse.cz> X-Mailer: Sylpheed 3.4.1 (GTK+ 2.24.23; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 11127 Lines: 231 On Tue, 29 Mar 2016 11:27:47 +0200 Vlastimil Babka wrote: > > v2: change more _count usages to _refcount > > There's also > Documentation/vm/transhuge.txt talking about ->_count > include/linux/mm.h: * requires to already have an elevated page->_count. > include/linux/mm_types.h: * Keep _count separate from slub cmpxchg_double data. > include/linux/mm_types.h: * slab_lock but _count is not. > include/linux/pagemap.h: * If the page is free (_count == 0), then _count is untouched, and 0 > include/linux/pagemap.h: * is returned. Otherwise, _count is incremented by 1 and 1 is returned. > include/linux/pagemap.h: * this allows allocators to use a synchronize_rcu() to stabilize _count. > include/linux/pagemap.h: * Remove-side that cares about stability of _count (eg. reclaim) has the > mm/huge_memory.c: * tail_page->_count is zero and not changing from under us. But > mm/huge_memory.c: /* Prevent deferred_split_scan() touching ->_count */ > mm/internal.h: * Turn a non-refcounted page (->_count == 0) into refcounted with > mm/page_alloc.c: bad_reason = "nonzero _count"; > mm/page_alloc.c: bad_reason = "nonzero _count"; > mm/page_alloc.c: * because their page->_count is zero at all time. > mm/slub.c: * as page->_count. If we assign to ->counters directly > mm/slub.c: * we run the risk of losing updates to page->_count, so > mm/vmscan.c: * load is not satisfied before that of page->_count. > mm/vmscan.c: * The downside is that we have to touch page->_count against each page. > > I've arrived at the following command to find this: > git grep "[^a-zA-Z0-9_]_count[^_]" > > Not that many false positives in the output :) From: Andrew Morton Subject: mm-rename-_count-field-of-the-struct-page-to-_refcount-fix fix comments, per Vlastimil Cc: Vlastimil Babka Cc: "David S. Miller" Cc: Chris Metcalf Cc: Hugh Dickins Cc: Johannes Berg Cc: Joonsoo Kim Cc: Sunil Goutham Signed-off-by: Andrew Morton --- drivers/block/aoe/aoecmd.c | 2 +- drivers/hwtracing/intel_th/msu.c | 2 +- fs/proc/page.c | 2 +- include/linux/mm.h | 2 +- include/linux/mm_types.h | 6 +++--- include/linux/pagemap.h | 8 ++++---- mm/huge_memory.c | 4 ++-- mm/internal.h | 2 +- mm/page_alloc.c | 2 +- mm/slub.c | 4 ++-- mm/vmscan.c | 4 ++-- 11 files changed, 19 insertions(+), 19 deletions(-) diff -puN drivers/block/aoe/aoecmd.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix drivers/block/aoe/aoecmd.c --- a/drivers/block/aoe/aoecmd.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/drivers/block/aoe/aoecmd.c @@ -861,7 +861,7 @@ rqbiocnt(struct request *r) * discussion. * * We cannot use get_page in the workaround, because it insists on a - * positive page count as a precondition. So we use _count directly. + * positive page count as a precondition. So we use _refcount directly. */ static void bio_pageinc(struct bio *bio) diff -puN drivers/hwtracing/intel_th/msu.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix drivers/hwtracing/intel_th/msu.c --- a/drivers/hwtracing/intel_th/msu.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/drivers/hwtracing/intel_th/msu.c @@ -1164,7 +1164,7 @@ static void msc_mmap_close(struct vm_are if (!atomic_dec_and_mutex_lock(&msc->mmap_count, &msc->buf_mutex)) return; - /* drop page _counts */ + /* drop page _refcounts */ for (pg = 0; pg < msc->nr_pages; pg++) { struct page *page = msc_buffer_get_page(msc, pg); diff -puN fs/proc/page.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix fs/proc/page.c --- a/fs/proc/page.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/fs/proc/page.c @@ -142,7 +142,7 @@ u64 stable_page_flags(struct page *page) /* - * Caveats on high order pages: page->_count will only be set + * Caveats on high order pages: page->_refcount will only be set * -1 on the head page; SLUB/SLQB do the same for PG_slab; * SLOB won't set PG_slab at all on compound pages. */ diff -puN include/linux/mm.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix include/linux/mm.h --- a/include/linux/mm.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/include/linux/mm.h @@ -721,7 +721,7 @@ static inline void get_page(struct page page = compound_head(page); /* * Getting a normal page or the head of a compound page - * requires to already have an elevated page->_count. + * requires to already have an elevated page->_refcount. */ VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page); page_ref_inc(page); diff -puN include/linux/mm_types.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix include/linux/mm_types.h --- a/include/linux/mm_types.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/include/linux/mm_types.h @@ -73,9 +73,9 @@ struct page { unsigned long counters; #else /* - * Keep _count separate from slub cmpxchg_double data. - * As the rest of the double word is protected by - * slab_lock but _count is not. + * Keep _refcount separate from slub cmpxchg_double + * data. As the rest of the double word is protected by + * slab_lock but _refcount is not. */ unsigned counters; #endif diff -puN include/linux/pagemap.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix include/linux/pagemap.h --- a/include/linux/pagemap.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/include/linux/pagemap.h @@ -105,12 +105,12 @@ void release_pages(struct page **pages, /* * speculatively take a reference to a page. - * If the page is free (_count == 0), then _count is untouched, and 0 - * is returned. Otherwise, _count is incremented by 1 and 1 is returned. + * If the page is free (_refcount == 0), then _refcount is untouched, and 0 + * is returned. Otherwise, _refcount is incremented by 1 and 1 is returned. * * This function must be called inside the same rcu_read_lock() section as has * been used to lookup the page in the pagecache radix-tree (or page table): - * this allows allocators to use a synchronize_rcu() to stabilize _count. + * this allows allocators to use a synchronize_rcu() to stabilize _refcount. * * Unless an RCU grace period has passed, the count of all pages coming out * of the allocator must be considered unstable. page_count may return higher @@ -126,7 +126,7 @@ void release_pages(struct page **pages, * 2. conditionally increment refcount * 3. check the page is still in pagecache (if no, goto 1) * - * Remove-side that cares about stability of _count (eg. reclaim) has the + * Remove-side that cares about stability of _refcount (eg. reclaim) has the * following (with tree_lock held for write): * A. atomically check refcount is correct and set it to 0 (atomic_cmpxchg) * B. remove page from pagecache diff -puN mm/huge_memory.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/huge_memory.c --- a/mm/huge_memory.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/mm/huge_memory.c @@ -3120,7 +3120,7 @@ static void __split_huge_page_tail(struc VM_BUG_ON_PAGE(page_ref_count(page_tail) != 0, page_tail); /* - * tail_page->_count is zero and not changing from under us. But + * tail_page->_refcount is zero and not changing from under us. But * get_page_unless_zero() may be running from under us on the * tail_page. If we used atomic_set() below instead of atomic_inc(), we * would then run atomic_set() concurrently with @@ -3289,7 +3289,7 @@ int split_huge_page_to_list(struct page if (mlocked) lru_add_drain(); - /* Prevent deferred_split_scan() touching ->_count */ + /* Prevent deferred_split_scan() touching ->_refcount */ spin_lock_irqsave(&pgdata->split_queue_lock, flags); count = page_count(head); mapcount = total_mapcount(head); diff -puN mm/internal.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/internal.h --- a/mm/internal.h~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/mm/internal.h @@ -58,7 +58,7 @@ static inline unsigned long ra_submit(st } /* - * Turn a non-refcounted page (->_count == 0) into refcounted with + * Turn a non-refcounted page (->_refcount == 0) into refcounted with * a count of one. */ static inline void set_page_refcounted(struct page *page) diff -puN mm/page_alloc.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/page_alloc.c --- a/mm/page_alloc.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/mm/page_alloc.c @@ -6864,7 +6864,7 @@ bool has_unmovable_pages(struct zone *zo * We can't use page_count without pin a page * because another CPU can free compound page. * This check already skips compound tails of THP - * because their page->_count is zero at all time. + * because their page->_refcount is zero at all time. */ if (!page_ref_count(page)) { if (PageBuddy(page)) diff -puN mm/slub.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/slub.c --- a/mm/slub.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/mm/slub.c @@ -329,8 +329,8 @@ static inline void set_page_slub_counter tmp.counters = counters_new; /* * page->counters can cover frozen/inuse/objects as well - * as page->_count. If we assign to ->counters directly - * we run the risk of losing updates to page->_count, so + * as page->_refcount. If we assign to ->counters directly + * we run the risk of losing updates to page->_refcount, so * be careful and only assign to the fields we need. */ page->frozen = tmp.frozen; diff -puN mm/vmscan.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix mm/vmscan.c --- a/mm/vmscan.c~mm-rename-_count-field-of-the-struct-page-to-_refcount-fix +++ a/mm/vmscan.c @@ -633,7 +633,7 @@ static int __remove_mapping(struct addre * * Reversing the order of the tests ensures such a situation cannot * escape unnoticed. The smp_rmb is needed to ensure the page->flags - * load is not satisfied before that of page->_count. + * load is not satisfied before that of page->_refcount. * * Note that if SetPageDirty is always performed via set_page_dirty, * and thus under tree_lock, then this ordering is not required. @@ -1720,7 +1720,7 @@ shrink_inactive_list(unsigned long nr_to * It is safe to rely on PG_active against the non-LRU pages in here because * nobody will play with that bit on a non-LRU page. * - * The downside is that we have to touch page->_count against each page. + * The downside is that we have to touch page->_refcount against each page. * But we had to alter page->flags anyway. */ _