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Concurency : sharing same memory space


Concurency : sharing same memory space

By : Roxanne
Date : November 21 2020, 09:01 AM
Hope that helps Problem solved : some of my buffers didn't even get the chance to get created because I was aborting the prepareForRendering function in some cases before the buffer creation part. Cases being : attempting to create texture ressources from file (CreateWICTextureFromFileEx https://msdn.microsoft.com/en-us/library/windows/desktop/ff476904%28v=vs.85%29.aspx).
My texture creation (all) failed unexpectedly because of the COM interface they require wasn't setup to work in multi-threaded mode (see - https://msdn.microsoft.com/en-us/library/windows/desktop/ms695279%28v=vs.85%29.aspx CoinitializeEx).
code :


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In memory mysql table vs redis about insert and concurency performance

In memory mysql table vs redis about insert and concurency performance


By : nl2br
Date : March 29 2020, 07:55 AM
To fix this issue Concurrency for the MySQL MEMORY storage engine is not good. Like MyISAM, it can only do table-locks. So all concurrent threads doing inserts queue up against each other.
Sharing memory from the linux kernel to user space in single user mode

Sharing memory from the linux kernel to user space in single user mode


By : MoWangChen
Date : March 29 2020, 07:55 AM
this one helps. "Single user mode" is a convention defined by userspace. It has no significance to the kernel; all of the same rules apply as "normal mode".
If you want to access memory -- any memory -- from userspace, you will need to map that memory into the process somehow. Using mmap() on a special file or device node is the most natural way of doing this.
Sharing memory from kernel to user space by disabling the "Write Protect Bit (CR0:16)"

Sharing memory from kernel to user space by disabling the "Write Protect Bit (CR0:16)"


By : Y05H10
Date : March 29 2020, 07:55 AM
this one helps. I just experimented on my own computer but to answer my own question: NO, it is not possible to share the kernel's memory directly with a user space process.
I did try to write my own kernel module based on Tempesta's stack-like region-based memory manager (pool.c):
code :
[...]

static int __init
tfw_pool_init(void)
{
    printk(KERN_ALERT "HIJACK INIT\n");
    write_cr0 (read_cr0 () & (~ 0x10000));

    pg_cache = alloc_percpu(unsigned long [TFW_POOL_PGCACHE_SZ]);
    if (pg_cache == NULL)
        return -ENOMEM;

    printk(KERN_NOTICE "__tfw_pool_new = %p\n", __tfw_pool_new);
    printk(KERN_NOTICE "tfw_pool_alloc = %p\n", tfw_pool_alloc);
    printk(KERN_NOTICE "tfw_pool_realloc = %p\n", tfw_pool_realloc);
    printk(KERN_NOTICE "tfw_pool_free = %p\n", tfw_pool_free);
    printk(KERN_NOTICE "tfw_pool_destroy = %p\n", tfw_pool_destroy);

    return 0;
}

static void __exit
tfw_pool_exit(void)
{
    free_percpu(pg_cache);

    write_cr0 (read_cr0 () | 0x10000);
    printk(KERN_ALERT "MODULE EXIT\n");
}

module_init(tfw_pool_init);
module_exit(tfw_pool_exit);
MODULE_LICENSE("GPL");
Sharing memory between user space and kernel space

Sharing memory between user space and kernel space


By : Murdoch
Date : March 29 2020, 07:55 AM
I hope this helps you . User mode side: There are a couple of ways.
1) The most common / flexible way is to use DeviceIOControl to communicate between user mode and kernel mode, including passing memory.
How user space memory and kernel space memory is mapped to physical memory in Linux?

How user space memory and kernel space memory is mapped to physical memory in Linux?


By : New2This
Date : March 29 2020, 07:55 AM
wish helps you
So What I understand is, for 32 bit architecture, we have 4 GB virtual memory, In which 3 GB is used for user space and 1 GB for kernel space.
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