linux-kernel - Re: [PATCH v2 2/2] PM: hibernate: add check of preallocate mem for image size pages

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Date:   Fri, 4 Nov 2022 15:27:58 +0800
From:   TGSP <tgsp002@...il.com>
To:     Jiri Slaby <jirislaby@...nel.org>, rafael@...nel.org,
        len.brown@...el.com, pavel@....cz, huanglei@...inos.cn
Cc:     xiongxin@...inos.cn, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] PM: hibernate: add check of preallocate mem for
 image size pages

在 2022/11/4 14:25, Jiri Slaby 写道:
> On 04. 11. 22, 6:41, TGSP wrote:
>> From: xiongxin <xiongxin@...inos.cn>
>>
>> Added a check on the return value of preallocate_image_highmem(). If
>> memory preallocate is insufficient, S4 cannot be done;
>>
>> I am playing 4K video on a machine with AMD or other graphics card and
>> only 8GiB memory, and the kernel is not configured with CONFIG_HIGHMEM.
>> When doing the S4 test, the analysis found that when the pages get from
>> minimum_image_size() is large enough, The preallocate_image_memory() and
>> preallocate_image_highmem() calls failed to obtain enough memory. Add
>> the judgment that memory preallocate is insufficient;
>>
>> The detailed debugging data is as follows:
>>
>> image_size: 3225923584, totalram_pages: 1968948 in
>> hibernate_reserved_size_init();
>>
>> in hibernate_preallocate_memory():
>> code pages = minimum_image_size(saveable) = 717992, at this time(line):
>> count: 2030858
>> avail_normal: 2053753
>> highmem: 0
>> totalreserve_pages: 22895
>> max_size: 1013336
>> size: 787579
>> saveable: 1819905
>>
>> When the code executes to:
>> pages = preallocate_image_memory(alloc, avail_normal), at that
>> time(line):
>> pages_highmem: 0
>> avail_normal: 1335761
>> alloc: 1017522
>> pages: 1017522
>>
>> So enter the else branch judged by (pages < alloc), When executed to
>> size = preallocate_image_memory(alloc, avail_normal):
>> alloc = max_size - size = 225757;
>> size = preallocate_image_memory(alloc, avail_normal) = 168671, That is,
>> preallocate_image_memory() does not apply for all alloc memory pages,
>> because highmem is not enabled, and size_highmem will return 0 here, so
>> there is a memory page that has not been preallocated, so I think a
>> judgment needs to be added here.
>>
>> But what I can't understand is that although pages are not preallocated
>> enough, "pages -= free_unnecessary_pages()" in the code below can also
>> discard some pages that have been preallocated, so I am not sure whether
>> it is appropriate to add a judgment here.
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: xiongxin <xiongxin@...inos.cn>
>> Signed-off-by: huanglei <huanglei@...inos.cn>
>> ---
>>   kernel/power/snapshot.c | 11 +++++++++--
>>   1 file changed, 9 insertions(+), 2 deletions(-)
>>
>> diff --git a/kernel/power/snapshot.c b/kernel/power/snapshot.c
>> index c20ca5fb9adc..546d544cf7de 100644
>> --- a/kernel/power/snapshot.c
>> +++ b/kernel/power/snapshot.c
>> @@ -1854,6 +1854,8 @@ int hibernate_preallocate_memory(void)
>>           alloc = (count - pages) - size;
>>           pages += preallocate_image_highmem(alloc);
>>       } else {
>> +        unsigned long size_highmem = 0;
> 
> This needs not be initialized, right?

If there is no need to make judgments here, then in the (pages < alloc) 
branch, it is necessary to make judgments on (pages_highmem < alloc)? 
should be the same;

> 
>> @@ -1863,8 +1865,13 @@ int hibernate_preallocate_memory(void)
>>           pages_highmem += size;
>>           alloc -= size;
>>           size = preallocate_image_memory(alloc, avail_normal);
>> -        pages_highmem += preallocate_image_highmem(alloc - size);
>> -        pages += pages_highmem + size;
>> +        size_highmem = preallocate_image_highmem(alloc - size);
>> +        if (size_highmem < (alloc - size)) {
>> +            pr_err("Image allocation is %lu pages short, exit\n",
>> +                alloc - size - pages_highmem);
>> +            goto err_out;
>> +        }
>> +        pages += pages_highmem + size_highmem + size;
>>       }
>>       /*
>