[CRIU] [PATCH 1/3] page-read: Do not lseek file to get its current position

[Mike Rapoport]

On Mon, Nov 14, 2016 at 2:58 PM, Pavel Emelyanov <xemul at virtuozzo.com> wrote:
> On 11/12/2016 04:35 PM, Mike Rapoport wrote:
>> On Wed, Nov 09, 2016 at 08:39:17PM +0200, Mike Rapoport wrote:
>>> On Mon, Nov 07, 2016 at 07:02:50PM +0300, Pavel Emelyanov wrote:
>>>> It's already written into page_read->pi_off, so just use one.
>>>>
>>>> Signed-off-by: Pavel Emelyanov <xemul at virtuozzo.com>
>>>
>>> Acked-by: Mike Rapoport <rppt at linux.vnet.ibm.com>
>>
>> Actually, not...
>> For cases when pages*img is randomly accessed, i.e. dedup and lazy-pages,
>> we still have to maintain actual position on the pages*img file and that
>> requires lseek. We can avoid lseek's for sequential reads if, say, we'll
>> add another pi_off_something to track actual position in the pages*img.
>
> Don't we ->reset the page-read in such cases? I thought we did...

Disregard this, I've missed s/read/pread.
There's v4 of the asyn page_read :)

>>>> ---
>>>>  criu/pagemap.c | 11 +++++------
>>>>  1 file changed, 5 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/criu/pagemap.c b/criu/pagemap.c
>>>> index 105ad59..cfc9659 100644
>>>> --- a/criu/pagemap.c
>>>> +++ b/criu/pagemap.c
>>>> @@ -260,23 +260,22 @@ static int read_pagemap_page(struct page_read *pr, unsigned long vaddr, int nr,
>>>>             BUG();
>>>>     } else {
>>>>             int fd = img_raw_fd(pr->pi);
>>>> -           off_t current_vaddr = lseek(fd, pr->pi_off, SEEK_SET);
>>>>
>>>> -           pr_debug("\tpr%u Read page from self %lx/%"PRIx64"\n", pr->id, pr->cvaddr, current_vaddr);
>>>> -           ret = read(fd, buf, len);
>>>> +           pr_debug("\tpr%u Read page from self %lx/%"PRIx64"\n", pr->id, pr->cvaddr, pr->pi_off);
>>>> +           ret = pread(fd, buf, len, pr->pi_off);
>>>>             if (ret != len) {
>>>>                     pr_perror("Can't read mapping page %d", ret);
>>>>                     return -1;
>>>>             }
>>>>
>>>> -           pr->pi_off += len;
>>>> -
>>>>             if (opts.auto_dedup) {
>>>> -                   ret = punch_hole(pr, current_vaddr, len, false);
>>>> +                   ret = punch_hole(pr, pr->pi_off, len, false);
>>>>                     if (ret == -1) {
>>>>                             return -1;
>>>>                     }
>>>>             }
>>>> +
>>>> +           pr->pi_off += len;
>>>>     }
>>>>
>>>>     pr->cvaddr += len;
>>>> --
>>>> 2.1.4
>>>>
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>>>>
>>>
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>>
>> .
>>
>
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-- 
Sincerely yours,
Mike.