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From: Andrew Morton <akpm@linux-foundation.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: <linux-mm@kvack.org>, Oscar Salvador <OSalvador@suse.com>,
	Baoquan He <bhe@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH 1/5] mm: print more information about mapping in __dump_page
Date: Fri, 23 Nov 2018 16:04:04 -0800	[thread overview]
Message-ID: <20181123160404.259413e56a8cc9a22112712a@linux-foundation.org> (raw)
In-Reply-To: <20181107101830.17405-2-mhocko@kernel.org>

On Wed,  7 Nov 2018 11:18:26 +0100 Michal Hocko <mhocko@kernel.org> wrote:

> From: Michal Hocko <mhocko@suse.com>
> 
> __dump_page prints the mapping pointer but that is quite unhelpful
> for many reports because the pointer itself only helps to distinguish
> anon/ksm mappings from other ones (because of lowest bits
> set). Sometimes it would be much more helpful to know what kind of
> mapping that is actually and if we know this is a file mapping then also
> try to resolve the dentry name.
> 
> ...
>
> --- a/mm/debug.c
> +++ b/mm/debug.c
>
> ...
>
> @@ -70,6 +71,18 @@ void __dump_page(struct page *page, const char *reason)
>  	if (PageCompound(page))
>  		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
>  	pr_cont("\n");
> +	if (PageAnon(page))
> +		pr_emerg("anon ");
> +	else if (PageKsm(page))
> +		pr_emerg("ksm ");
> +	else if (mapping) {
> +		pr_emerg("%ps ", mapping->a_ops);
> +		if (mapping->host->i_dentry.first) {
> +			struct dentry *dentry;
> +			dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias);
> +			pr_emerg("name:\"%*s\" ", dentry->d_name.len, dentry->d_name.name);
> +		}
> +	}

There has to be a better way of printing the filename.  It is so often
needed.

The (poorly named and gleefully undocumented)
take_dentry_name_snapshot() looks promising.  However it's unclear that
__dump_page() is always called from contexts where
take_dentry_name_snapshot() and release_dentry_name_snapshot() can be
safely called.  Probably it's OK, but how to guarantee it?



WARNING: multiple messages have this Message-ID
From: Andrew Morton <akpm@linux-foundation.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: linux-mm@kvack.org, Oscar Salvador <OSalvador@suse.com>,
	Baoquan He <bhe@redhat.com>, LKML <linux-kernel@vger.kernel.org>,
	Michal Hocko <mhocko@suse.com>
Subject: Re: [RFC PATCH 1/5] mm: print more information about mapping in __dump_page
Date: Fri, 23 Nov 2018 16:04:04 -0800	[thread overview]
Message-ID: <20181123160404.259413e56a8cc9a22112712a@linux-foundation.org> (raw)
In-Reply-To: <20181107101830.17405-2-mhocko@kernel.org>

On Wed,  7 Nov 2018 11:18:26 +0100 Michal Hocko <mhocko@kernel.org> wrote:

> From: Michal Hocko <mhocko@suse.com>
> 
> __dump_page prints the mapping pointer but that is quite unhelpful
> for many reports because the pointer itself only helps to distinguish
> anon/ksm mappings from other ones (because of lowest bits
> set). Sometimes it would be much more helpful to know what kind of
> mapping that is actually and if we know this is a file mapping then also
> try to resolve the dentry name.
> 
> ...
>
> --- a/mm/debug.c
> +++ b/mm/debug.c
>
> ...
>
> @@ -70,6 +71,18 @@ void __dump_page(struct page *page, const char *reason)
>  	if (PageCompound(page))
>  		pr_cont(" compound_mapcount: %d", compound_mapcount(page));
>  	pr_cont("\n");
> +	if (PageAnon(page))
> +		pr_emerg("anon ");
> +	else if (PageKsm(page))
> +		pr_emerg("ksm ");
> +	else if (mapping) {
> +		pr_emerg("%ps ", mapping->a_ops);
> +		if (mapping->host->i_dentry.first) {
> +			struct dentry *dentry;
> +			dentry = container_of(mapping->host->i_dentry.first, struct dentry, d_u.d_alias);
> +			pr_emerg("name:\"%*s\" ", dentry->d_name.len, dentry->d_name.name);
> +		}
> +	}

There has to be a better way of printing the filename.  It is so often
needed.

The (poorly named and gleefully undocumented)
take_dentry_name_snapshot() looks promising.  However it's unclear that
__dump_page() is always called from contexts where
take_dentry_name_snapshot() and release_dentry_name_snapshot() can be
safely called.  Probably it's OK, but how to guarantee it?

  reply	other threads:[~2018-11-24  0:04 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-07 10:18 [RFC PATCH 0/5] mm, memory_hotplug: improve memory offlining failures debugging Michal Hocko
2018-11-07 10:18 ` Michal Hocko
2018-11-07 10:18 ` [RFC PATCH 1/5] mm: print more information about mapping in __dump_page Michal Hocko
2018-11-07 10:18   ` Michal Hocko
2018-11-24  0:04   ` Andrew Morton [this message]
2018-11-24  0:04     ` Andrew Morton
2018-11-25  8:10     ` Michal Hocko
2018-11-07 10:18 ` [RFC PATCH 2/5] mm: lower the printk loglevel for __dump_page messages Michal Hocko
2018-11-07 10:18   ` Michal Hocko
2018-11-16  0:56   ` Baoquan He
2018-12-12 14:25   ` Michal Hocko
2018-12-12 14:34     ` Michal Hocko
2018-11-07 10:18 ` [RFC PATCH 3/5] mm, memory_hotplug: drop pointless block alignment checks from __offline_pages Michal Hocko
2018-11-07 10:18   ` Michal Hocko
2018-11-07 10:18 ` [RFC PATCH 4/5] mm, memory_hotplug: print reason for the offlining failure Michal Hocko
2018-11-07 10:18   ` Michal Hocko
2018-11-07 22:04   ` Andrew Morton
2018-11-07 22:04     ` Andrew Morton
2018-11-08  8:01     ` Michal Hocko
2018-11-13  8:02     ` Michal Hocko
2018-11-08  6:23   ` Anshuman Khandual
2018-11-08  7:59     ` Michal Hocko
2018-11-07 10:18 ` [RFC PATCH 5/5] mm, memory_hotplug: be more verbose for memory offline failures Michal Hocko
2018-11-07 10:18   ` Michal Hocko
2018-11-08  7:16   ` Anshuman Khandual
2018-11-08  8:12     ` Michal Hocko
2018-11-08  8:19       ` Anshuman Khandual
2018-11-13  8:03       ` Michal Hocko
2018-11-16  0:07   ` Andrew Morton
2018-11-16  0:07     ` Andrew Morton
2018-11-16  7:21     ` Michal Hocko
2018-11-16  7:21       ` Michal Hocko

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