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Date: Tue, 20 Aug 2013 16:09:22 +0800
From: Chen Gang <gang.chen@...anux.com>
To: Cyrill Gorcunov <gorcunov@...il.com>
CC: 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 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 */
>>>
>>>
>>>
>>
>>
>
>
--
Chen Gang
--
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