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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BA91FC433F5 for ; Thu, 18 Nov 2021 09:22:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 96AD561B95 for ; Thu, 18 Nov 2021 09:22:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245124AbhKRJZo (ORCPT ); Thu, 18 Nov 2021 04:25:44 -0500 Received: from smtp-out1.suse.de ([195.135.220.28]:50924 "EHLO smtp-out1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241323AbhKRJZh (ORCPT ); Thu, 18 Nov 2021 04:25:37 -0500 Received: from relay2.suse.de (relay2.suse.de [149.44.160.134]) by smtp-out1.suse.de (Postfix) with ESMTP id 48E1321763; Thu, 18 Nov 2021 09:22:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1637227357; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=q6iiWQeeIKLNGLnUwc8/VbB9r+gV+5b2XZV6BZvYfco=; b=kecWV1Ad/JRMeprX80gouQRTuyWFJjecbRj2QGb7406UCMNuemOzEqK4qPtiN3vr0Bkeo+ VigrxkcImtS51/CliB4OoDpfyIzMgUCq3imyADdiv/4c/uNGOIoThG1QZA1FRHaUUI9+Fk zBf/JE719T4ZUrTU9Udc9PTGFThXgX0= Received: from suse.cz (unknown [10.100.201.86]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by relay2.suse.de (Postfix) with ESMTPS id 15D1AA3B81; Thu, 18 Nov 2021 09:22:37 +0000 (UTC) Date: Thu, 18 Nov 2021 10:22:36 +0100 From: Michal Hocko To: NeilBrown Cc: Andrew Morton , Thierry Reding , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mel Gorman Subject: Re: [PATCH] MM: discard __GFP_ATOMIC Message-ID: References: <163712397076.13692.4727608274002939094@noble.neil.brown.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <163712397076.13692.4727608274002939094@noble.neil.brown.name> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [Cc Mel] On Wed 17-11-21 15:39:30, Neil Brown wrote: > > __GFP_ATOMIC serves little purpose. > It's main effect is to set ALLOC_HARDER which adds a few little boosts to > increase the chance of an allocation succeeding, one of which is to > lower the water-mark at which it will succeed. > > It is *always* paired with __GFP_HIGH which sets ALLOC_HIGH which also > adjusts this watermark. It is probable that other users of __GFP_HIGH > should benefit from the other little bonuses that __GFP_ATOMIC gets. > > __GFP_ATOMIC also gives a warning if used with __GFP_DIRECT_RECLAIM. > There is little point to this. We already get a might_sleep() warning > if __GFP_DIRECT_RECLAIM is set. > > __GFP_ATOMIC allows the "watermark_boost" to be side-stepped. It is > probable that testing ALLOC_HARDER is a better fit here. > > __GFP_ATOMIC is used by tegra-smmu.c to check if the allocation might > sleep. This should test __GFP_DIRECT_RECLAIM instead. > > This patch: > - removes __GFP_ATOMIC > - causes __GFP_HIGH to set ALLOC_HARDER unless __GFP_NOMEMALLOC is set > (as well as ALLOC_HIGH). > - makes other adjustments as suggested by the above. > > The net result is not change to GFP_ATOMIC allocations. Other > allocations that use __GFP_HIGH will benefit from a few different extra > privileges. This affects: > xen, dm, md, ntfs3 > the vermillion frame buffer > hibernation > ksm > swap > all of which likely produce more benefit than cost if these selected > allocation are more likely to succeed quickly. > > Signed-off-by: NeilBrown > --- > > This patch came out of my attempts to review and document some of the > __GFP flags. I couldn't find that __GFP_ATOMIC meant anything really > useful, so I thought that discarding it would be best. > > Obviously GFP_ATOMIC is useful - just not __GFP_ATOMIC (and the fact > that both names exist could be seen as a warning sign). > > Thanks, > NeilBrown > > > Documentation/vm/balance.rst | 2 +- > drivers/iommu/tegra-smmu.c | 4 ++-- > include/linux/gfp.h | 12 ++++-------- > include/trace/events/mmflags.h | 1 - > lib/test_printf.c | 8 ++++---- > mm/internal.h | 3 +-- > mm/memcontrol.c | 2 +- > mm/page_alloc.c | 16 ++++------------ > tools/perf/builtin-kmem.c | 1 - > tools/testing/radix-tree/linux/gfp.h | 3 +-- > 10 files changed, 18 insertions(+), 34 deletions(-) > > diff --git a/Documentation/vm/balance.rst b/Documentation/vm/balance.rst > index 6a1fadf3e173..e38e9d83c1c7 100644 > --- a/Documentation/vm/balance.rst > +++ b/Documentation/vm/balance.rst > @@ -6,7 +6,7 @@ Memory Balancing > > Started Jan 2000 by Kanoj Sarcar > > -Memory balancing is needed for !__GFP_ATOMIC and !__GFP_KSWAPD_RECLAIM as > +Memory balancing is needed for !__GFP_HIGH and !__GFP_KSWAPD_RECLAIM as > well as for non __GFP_IO allocations. > > The first reason why a caller may avoid reclaim is that the caller can not > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c > index e900e3c46903..c5fa8b8673b6 100644 > --- a/drivers/iommu/tegra-smmu.c > +++ b/drivers/iommu/tegra-smmu.c > @@ -676,12 +676,12 @@ static struct page *as_get_pde_page(struct tegra_smmu_as *as, > * allocate page in a sleeping context if GFP flags permit. Hence > * spinlock needs to be unlocked and re-locked after allocation. > */ > - if (!(gfp & __GFP_ATOMIC)) > + if (gfp & __GFP_DIRECT_RECLAIM) > spin_unlock_irqrestore(&as->lock, *flags); > > page = alloc_page(gfp | __GFP_DMA | __GFP_ZERO); > > - if (!(gfp & __GFP_ATOMIC)) > + if (gfp & __GFP_DIRECT_RECLAIM) > spin_lock_irqsave(&as->lock, *flags); > > /* > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index b976c4177299..676c813bd93f 100644 > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -39,7 +39,7 @@ struct vm_area_struct; > #define ___GFP_IO 0x40u > #define ___GFP_FS 0x80u > #define ___GFP_ZERO 0x100u > -#define ___GFP_ATOMIC 0x200u > +/* 0x200u unused */ > #define ___GFP_DIRECT_RECLAIM 0x400u > #define ___GFP_KSWAPD_RECLAIM 0x800u > #define ___GFP_WRITE 0x1000u > @@ -116,11 +116,8 @@ struct vm_area_struct; > * > * %__GFP_HIGH indicates that the caller is high-priority and that granting > * the request is necessary before the system can make forward progress. > - * For example, creating an IO context to clean pages. > - * > - * %__GFP_ATOMIC indicates that the caller cannot reclaim or sleep and is > - * high priority. Users are typically interrupt handlers. This may be > - * used in conjunction with %__GFP_HIGH > + * For example creating an IO context to clean pages and requests > + * from atomic context. > * > * %__GFP_MEMALLOC allows access to all memory. This should only be used when > * the caller guarantees the allocation will allow more memory to be freed > @@ -135,7 +132,6 @@ struct vm_area_struct; > * %__GFP_NOMEMALLOC is used to explicitly forbid access to emergency reserves. > * This takes precedence over the %__GFP_MEMALLOC flag if both are set. > */ > -#define __GFP_ATOMIC ((__force gfp_t)___GFP_ATOMIC) > #define __GFP_HIGH ((__force gfp_t)___GFP_HIGH) > #define __GFP_MEMALLOC ((__force gfp_t)___GFP_MEMALLOC) > #define __GFP_NOMEMALLOC ((__force gfp_t)___GFP_NOMEMALLOC) > @@ -320,7 +316,7 @@ struct vm_area_struct; > * version does not attempt reclaim/compaction at all and is by default used > * in page fault path, while the non-light is used by khugepaged. > */ > -#define GFP_ATOMIC (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM) > +#define GFP_ATOMIC (__GFP_HIGH|__GFP_KSWAPD_RECLAIM) > #define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS) > #define GFP_KERNEL_ACCOUNT (GFP_KERNEL | __GFP_ACCOUNT) > #define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM) > diff --git a/include/trace/events/mmflags.h b/include/trace/events/mmflags.h > index 116ed4d5d0f8..30f492256b8c 100644 > --- a/include/trace/events/mmflags.h > +++ b/include/trace/events/mmflags.h > @@ -29,7 +29,6 @@ > {(unsigned long)__GFP_HIGHMEM, "__GFP_HIGHMEM"}, \ > {(unsigned long)GFP_DMA32, "GFP_DMA32"}, \ > {(unsigned long)__GFP_HIGH, "__GFP_HIGH"}, \ > - {(unsigned long)__GFP_ATOMIC, "__GFP_ATOMIC"}, \ > {(unsigned long)__GFP_IO, "__GFP_IO"}, \ > {(unsigned long)__GFP_FS, "__GFP_FS"}, \ > {(unsigned long)__GFP_NOWARN, "__GFP_NOWARN"}, \ > diff --git a/lib/test_printf.c b/lib/test_printf.c > index 07309c45f327..8010de49b6c5 100644 > --- a/lib/test_printf.c > +++ b/lib/test_printf.c > @@ -673,17 +673,17 @@ flags(void) > gfp = GFP_ATOMIC|__GFP_DMA; > test("GFP_ATOMIC|GFP_DMA", "%pGg", &gfp); > > - gfp = __GFP_ATOMIC; > - test("__GFP_ATOMIC", "%pGg", &gfp); > + gfp = __GFP_HIGH; > + test("__GFP_HIGH", "%pGg", &gfp); > > /* Any flags not translated by the table should remain numeric */ > gfp = ~__GFP_BITS_MASK; > snprintf(cmp_buffer, BUF_SIZE, "%#lx", (unsigned long) gfp); > test(cmp_buffer, "%pGg", &gfp); > > - snprintf(cmp_buffer, BUF_SIZE, "__GFP_ATOMIC|%#lx", > + snprintf(cmp_buffer, BUF_SIZE, "__GFP_HIGH|%#lx", > (unsigned long) gfp); > - gfp |= __GFP_ATOMIC; > + gfp |= __GFP_HIGH; > test(cmp_buffer, "%pGg", &gfp); > > kfree(cmp_buffer); > diff --git a/mm/internal.h b/mm/internal.h > index 3b79a5c9427a..4564067065f9 100644 > --- a/mm/internal.h > +++ b/mm/internal.h > @@ -20,8 +20,7 @@ > */ > #define GFP_RECLAIM_MASK (__GFP_RECLAIM|__GFP_HIGH|__GFP_IO|__GFP_FS|\ > __GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_NOFAIL|\ > - __GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC|\ > - __GFP_ATOMIC) > + __GFP_NORETRY|__GFP_MEMALLOC|__GFP_NOMEMALLOC) > > /* The GFP flags allowed during early boot */ > #define GFP_BOOT_MASK (__GFP_BITS_MASK & ~(__GFP_RECLAIM|__GFP_IO|__GFP_FS)) > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 781605e92015..1ff55347e4b9 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -2621,7 +2621,7 @@ static int try_charge_memcg(struct mem_cgroup *memcg, gfp_t gfp_mask, > * put the burden of reclaim on regular allocation requests > * and let these go through as privileged allocations. > */ > - if (gfp_mask & __GFP_ATOMIC) > + if (gfp_mask & __GFP_HIGH) > goto force; > > /* > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index c5952749ad40..4fff90ca145b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3932,12 +3932,12 @@ static inline bool zone_watermark_fast(struct zone *z, unsigned int order, > free_pages)) > return true; > /* > - * Ignore watermark boosting for GFP_ATOMIC order-0 allocations > + * Ignore watermark boosting for GFP_HIGH order-0 allocations > * when checking the min watermark. The min watermark is the > * point where boosting is ignored so that kswapd is woken up > * when below the low watermark. > */ > - if (unlikely(!order && (gfp_mask & __GFP_ATOMIC) && z->watermark_boost > + if (unlikely(!order && (alloc_flags & ALLOC_HARDER) && z->watermark_boost > && ((alloc_flags & ALLOC_WMARK_MASK) == WMARK_MIN))) { > mark = z->_watermark[WMARK_MIN]; > return __zone_watermark_ok(z, order, mark, highest_zoneidx, > @@ -4661,12 +4661,12 @@ gfp_to_alloc_flags(gfp_t gfp_mask) > * The caller may dip into page reserves a bit more if the caller > * cannot run direct reclaim, or if the caller has realtime scheduling > * policy or is asking for __GFP_HIGH memory. GFP_ATOMIC requests will > - * set both ALLOC_HARDER (__GFP_ATOMIC) and ALLOC_HIGH (__GFP_HIGH). > + * set both ALLOC_HARDER (unless __GFP_NOMEMALLOC) and ALLOC_HIGH. > */ > alloc_flags |= (__force int) > (gfp_mask & (__GFP_HIGH | __GFP_KSWAPD_RECLAIM)); > > - if (gfp_mask & __GFP_ATOMIC) { > + if (gfp_mask & __GFP_HIGH) { > /* > * Not worth trying to allocate harder for __GFP_NOMEMALLOC even > * if it can't schedule. > @@ -4859,14 +4859,6 @@ __alloc_pages_slowpath(gfp_t gfp_mask, unsigned int order, > unsigned int cpuset_mems_cookie; > int reserve_flags; > > - /* > - * We also sanity check to catch abuse of atomic reserves being used by > - * callers that are not in atomic context. > - */ > - if (WARN_ON_ONCE((gfp_mask & (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM)) == > - (__GFP_ATOMIC|__GFP_DIRECT_RECLAIM))) > - gfp_mask &= ~__GFP_ATOMIC; > - > retry_cpuset: > compaction_retries = 0; > no_progress_loops = 0; > diff --git a/tools/perf/builtin-kmem.c b/tools/perf/builtin-kmem.c > index da03a341c63c..17e6eeb6e196 100644 > --- a/tools/perf/builtin-kmem.c > +++ b/tools/perf/builtin-kmem.c > @@ -640,7 +640,6 @@ static const struct { > { "__GFP_HIGHMEM", "HM" }, > { "GFP_DMA32", "D32" }, > { "__GFP_HIGH", "H" }, > - { "__GFP_ATOMIC", "_A" }, > { "__GFP_IO", "I" }, > { "__GFP_FS", "F" }, > { "__GFP_NOWARN", "NWR" }, > diff --git a/tools/testing/radix-tree/linux/gfp.h b/tools/testing/radix-tree/linux/gfp.h > index 32159c08a52e..0a0741104dfe 100644 > --- a/tools/testing/radix-tree/linux/gfp.h > +++ b/tools/testing/radix-tree/linux/gfp.h > @@ -12,7 +12,6 @@ > #define __GFP_FS 0x80u > #define __GFP_NOWARN 0x200u > #define __GFP_ZERO 0x8000u > -#define __GFP_ATOMIC 0x80000u > #define __GFP_ACCOUNT 0x100000u > #define __GFP_DIRECT_RECLAIM 0x400000u > #define __GFP_KSWAPD_RECLAIM 0x2000000u > @@ -20,7 +19,7 @@ > #define __GFP_RECLAIM (__GFP_DIRECT_RECLAIM|__GFP_KSWAPD_RECLAIM) > > #define GFP_ZONEMASK 0x0fu > -#define GFP_ATOMIC (__GFP_HIGH|__GFP_ATOMIC|__GFP_KSWAPD_RECLAIM) > +#define GFP_ATOMIC (__GFP_HIGH|__GFP_KSWAPD_RECLAIM) > #define GFP_KERNEL (__GFP_RECLAIM | __GFP_IO | __GFP_FS) > #define GFP_NOWAIT (__GFP_KSWAPD_RECLAIM) > > -- > 2.33.1 -- Michal Hocko SUSE Labs