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Message-ID: <52132523.6040702@gmail.com>
Date: Tue, 20 Aug 2013 16:13:23 +0800
From: Chen Gang F T <chen.gang.flying.transformer@...il.com>
To: Chen Gang <gang.chen@...anux.com>
CC: Cyrill Gorcunov <gorcunov@...il.com>, Mel Gorman <mgorman@...e.de>,
kosaki.motohiro@...fujitsu.com, riel@...hat.com, hughd@...gle.com,
xemul@...allels.com, rientjes@...gle.com,
Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 0/3] mm: mempolicy: the failure processing about mpol_to_str()
On 08/20/2013 04:09 PM, Chen Gang wrote:
> On 08/20/2013 03:51 PM, Chen Gang wrote:
>> On 08/20/2013 03:48 PM, Chen Gang wrote:
>>> On 08/20/2013 02:47 PM, Cyrill Gorcunov wrote:
>>>> On Tue, Aug 20, 2013 at 01:41:40PM +0800, Chen Gang wrote:
>>>>>
>>>>>> sure you'll have to change shmem_show_mpol statement to return int code.
>>>>>> Won't this be more short and convenient?
>>>>>>
>>>>>>
>>>>>
>>>>> Hmm... if return -ENOSPC, in common processing, it still need continue
>>>>> (but need let outside know about the string truncation).
>>>>>
>>>>> So I still suggest to give more check for it.
>>>>
>>>> I still don't like adding additional code like
>>>>
>>>> + ret = mpol_to_str(buffer, sizeof(buffer), mpol);
>>>> + if (ret < 0)
>>>> + switch (ret) {
>>>> + case -ENOSPC:
>>>> + printk(KERN_WARNING
>>>> + "in %s: string is truncated in mpol_to_str().\n",
>>>> + __func__);
>>
>> Oh, that need 'break' in my original patch. :-)
>>
>>>> + default:
>>>> + printk(KERN_ERR
>>>> + "in %s: call mpol_to_str() fail, errcode: %d. buffer: %p, size: %zu, pol: %p\n",
>>>> + __func__, ret, buffer, sizeof(buffer), mpol);
>>>> + return;
>>>> + }
>>>>
>>>> this code is pretty neat for debugging purpose I think but in most case (if
>>>> only I've not missed something obvious) it simply won't be the case.
>>>>
>>>
>>> For mpol_to_str(), it is for printing string, I suggest to fill buffer
>>> as full as possible like another printing string functions, -ENOSPC is
>>> not critical error, callers may can bear it, and still want to continue.
>>>
>>> For 2 callers, I still suggest to process '-ENOSPC' and continue, it is
>>> really not a critical error, they can continue.
>>>
>>> For the 'default' error processing:
>>>
>>> I still suggest to 'printk' in shmem_show_mpol(), because when failure occurs, it has no return value to mark the failure to upper caller.
>>> Hmm... but for show_numa_map(), may remove the 'printk', only return the error code is OK. :-)
>>>
>>>
>>> Thanks.
>>>
>
> Oh, for '-ENOSPC', it means critical error, it is my fault.
>
> So, for simplify thinking and implementation, use your patch below is OK
> to me (but I suggest to print error information in the none return value
> function).
>
> :-)
>
>>>> Won't somthing like below do the same but with smaller code change?
>>>> Note I've not even compiled it but it shows the idea.
>>>> ---
>>>> fs/proc/task_mmu.c | 4 +++-
>>>> mm/shmem.c | 17 +++++++++--------
>>>> 2 files changed, 12 insertions(+), 9 deletions(-)
>>>>
>>>> Index: linux-2.6.git/fs/proc/task_mmu.c
>>>> ===================================================================
>>>> --- linux-2.6.git.orig/fs/proc/task_mmu.c
>>>> +++ linux-2.6.git/fs/proc/task_mmu.c
>>>> @@ -1402,8 +1402,10 @@ static int show_numa_map(struct seq_file
>>>> walk.mm = mm;
>>>>
>>>> pol = get_vma_policy(task, vma, vma->vm_start);
>>>> - mpol_to_str(buffer, sizeof(buffer), pol);
>>>> + n = mpol_to_str(buffer, sizeof(buffer), pol);
>>>> mpol_cond_put(pol);
>>>> + if (n < 0)
>>>> + return n;
>>>>
>>>> seq_printf(m, "%08lx %s", vma->vm_start, buffer);
>>>>
>>>> Index: linux-2.6.git/mm/shmem.c
>>>> ===================================================================
>>>> --- linux-2.6.git.orig/mm/shmem.c
>>>> +++ linux-2.6.git/mm/shmem.c
>>>> @@ -883,16 +883,20 @@ redirty:
>>>>
>>>> #ifdef CONFIG_NUMA
>>>> #ifdef CONFIG_TMPFS
>>>> -static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>>>> +static int shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>>>> {
>>>> char buffer[64];
>>>> + int ret;
>>>>
>>>> if (!mpol || mpol->mode == MPOL_DEFAULT)
>>>> - return; /* show nothing */
>>>> + return 0; /* show nothing */
>>>>
>>>> - mpol_to_str(buffer, sizeof(buffer), mpol);
>>>> + ret = mpol_to_str(buffer, sizeof(buffer), mpol);
>>>> + if (ret < 0)
>>>> + return ret;
>>>>
>>>> seq_printf(seq, ",mpol=%s", buffer);
>>>> + return 0;
>>>> }
>>>>
>>>> static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
>>>> @@ -951,9 +955,7 @@ static struct page *shmem_alloc_page(gfp
>>>> }
>>>> #else /* !CONFIG_NUMA */
>>>> #ifdef CONFIG_TMPFS
>>>> -static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
>>>> -{
>>>> -}
>>>> +static inline int shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol) { return 0; }
>>>> #endif /* CONFIG_TMPFS */
>>>>
>>>> static inline struct page *shmem_swapin(swp_entry_t swap, gfp_t gfp,
>>>> @@ -2577,8 +2579,7 @@ static int shmem_show_options(struct seq
>>>> if (!gid_eq(sbinfo->gid, GLOBAL_ROOT_GID))
>>>> seq_printf(seq, ",gid=%u",
>>>> from_kgid_munged(&init_user_ns, sbinfo->gid));
>>>> - shmem_show_mpol(seq, sbinfo->mpol);
>>>> - return 0;
>>>> + return shmem_show_mpol(seq, sbinfo->mpol);
>>>> }
>>>> #endif /* CONFIG_TMPFS */
>>>>
>>>>
>>>>
Oh, you have done, sorry.
>>>
>>>
>>
>>
>
>
--
Chen Gang
--
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