linux-kernel - Re: [RFC PATCH 10/30] mm: enable page allocation tagging for __get_free_pages and alloc

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Date:   Wed, 31 Aug 2022 18:07:43 -0700
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Kent Overstreet <kent.overstreet@...ux.dev>
Cc:     Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Johannes Weiner <hannes@...xchg.org>,
        Roman Gushchin <roman.gushchin@...ux.dev>,
        Davidlohr Bueso <dave@...olabs.net>,
        Matthew Wilcox <willy@...radead.org>,
        "Liam R. Howlett" <liam.howlett@...cle.com>,
        David Vernet <void@...ifault.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Laurent Dufour <ldufour@...ux.ibm.com>,
        Peter Xu <peterx@...hat.com>,
        David Hildenbrand <david@...hat.com>,
        Jens Axboe <axboe@...nel.dk>, mcgrof@...nel.org,
        masahiroy@...nel.org, nathan@...nel.org, changbin.du@...el.com,
        ytcoode@...il.com, Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Benjamin Segall <bsegall@...gle.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Valentin Schneider <vschneid@...hat.com>,
        Christopher Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, 42.hyeyoo@...il.com,
        Alexander Potapenko <glider@...gle.com>,
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        Muchun Song <songmuchun@...edance.com>, arnd@...db.de,
        jbaron@...mai.com, David Rientjes <rientjes@...gle.com>,
        Minchan Kim <minchan@...gle.com>,
        Kalesh Singh <kaleshsingh@...gle.com>,
        kernel-team <kernel-team@...roid.com>,
        linux-mm <linux-mm@...ck.org>, iommu@...ts.linux.dev,
        kasan-dev@...glegroups.com, io-uring@...r.kernel.org,
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        linux-bcache@...r.kernel.org, linux-modules@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 10/30] mm: enable page allocation tagging for
 __get_free_pages and alloc_pages

On Wed, Aug 31, 2022 at 10:46 AM Kent Overstreet
<kent.overstreet@...ux.dev> wrote:
>
> On Wed, Aug 31, 2022 at 11:11:03AM +0100, Mel Gorman wrote:
> > On Tue, Aug 30, 2022 at 02:48:59PM -0700, Suren Baghdasaryan wrote:
> > > Redefine alloc_pages, __get_free_pages to record allocations done by
> > > these functions. Instrument deallocation hooks to record object freeing.
> > >
> > > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> > > +#ifdef CONFIG_PAGE_ALLOC_TAGGING
> > > +
> > >  #include <linux/alloc_tag.h>
> > >  #include <linux/page_ext.h>
> > >
> > > @@ -25,4 +27,37 @@ static inline void pgalloc_tag_dec(struct page *page, unsigned int order)
> > >             alloc_tag_sub(get_page_tag_ref(page), PAGE_SIZE << order);
> > >  }
> > >
> > > +/*
> > > + * Redefinitions of the common page allocators/destructors
> > > + */
> > > +#define pgtag_alloc_pages(gfp, order)                                      \
> > > +({                                                                 \
> > > +   struct page *_page = _alloc_pages((gfp), (order));              \
> > > +                                                                   \
> > > +   if (_page)                                                      \
> > > +           alloc_tag_add(get_page_tag_ref(_page), PAGE_SIZE << (order));\
> > > +   _page;                                                          \
> > > +})
> > > +
> >
> > Instead of renaming alloc_pages, why is the tagging not done in
> > __alloc_pages()? At least __alloc_pages_bulk() is also missed. The branch
> > can be guarded with IS_ENABLED.
>
> It can't be in a function, it has to be in a wrapper macro.

Ah, right. __FILE__, __LINE__ and others we use to record the call
location would point to include/linux/gfp.h instead of the location
allocation is performed at.

>
> alloc_tag_add() is a macro that defines a static struct in a special elf
> section. That struct holds the allocation counters, and putting it in a special
> elf section is how the code to list it in debugfs finds it.
>
> Look at the dynamic debug code for prior precedence for this trick in the kernel
> - that's how it makes pr_debug() calls dynamically controllable at runtime, from
> debugfs. We're taking that method and turning it into a proper library.
>
> Because all the counters are statically allocated, without even a pointer deref
> to get to them in the allocation path (one pointer deref to get to them in the
> deallocate path), that makes this _much, much_ cheaper than anything that could
> be done with tracing - cheap enough that I expect many users will want to enable
> it in production.
>
> --
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>