How to implement fork() without CoW properly?
I made a new syscall which is exactly the same as fork() except without CoW. Sadly, I've never experienced hacking the kernel so the new syscall made an error like below.
BUG: Bad rss-counter state mm:ffff8d56199c2640 idx:1 val:-18
I'm sure that this must be the tip of the iceberg of my broken syscall. Thus, before I will dig out the hidden or potential errors, I'd like to know what should be considered when making fork() without CoW or few tips.
The design of the new syscall is based on do_wp_page() -> wp_page_copy() in mm/memory.c. And I only give a change on copy_one_pte() because the calling functions such as copy_pte_range(), copy_pmd_range(), and etc would be the same as far as I thought.
The reason why I chose this function is that it is one of the page faults function to copy a page of CoW. I thought that I could make a similar one but I ended up confronting a lot function that I don't know and I found myself that I don't know how to check my new fork correctly copies all the pages of parents.
You might wonder why I am doing this. I know that fork() without CoW can make the worst performance when it happens. I just wanted to know that how much fast or slow between fork() and fork w/o CoW.
linux kernel x86
asked 6 mins ago
Mr.NobodyMr.Nobody
435
add a comment |
I made a new syscall which is exactly the same as fork() except without CoW. Sadly, I've never experienced hacking the kernel so the new syscall made an error like below.
BUG: Bad rss-counter state mm:ffff8d56199c2640 idx:1 val:-18
I'm sure that this must be the tip of the iceberg of my broken syscall. Thus, before I will dig out the hidden or potential errors, I'd like to know what should be considered when making fork() without CoW or few tips.
The design of the new syscall is based on do_wp_page() -> wp_page_copy() in mm/memory.c. And I only give a change on copy_one_pte() because the calling functions such as copy_pte_range(), copy_pmd_range(), and etc would be the same as far as I thought.
The reason why I chose this function is that it is one of the page faults function to copy a page of CoW. I thought that I could make a similar one but I ended up confronting a lot function that I don't know and I found myself that I don't know how to check my new fork correctly copies all the pages of parents.
You might wonder why I am doing this. I know that fork() without CoW can make the worst performance when it happens. I just wanted to know that how much fast or slow between fork() and fork w/o CoW.
linux kernel x86
asked 6 mins ago
Mr.NobodyMr.Nobody
435
add a comment |
I made a new syscall which is exactly the same as fork() except without CoW. Sadly, I've never experienced hacking the kernel so the new syscall made an error like below.
BUG: Bad rss-counter state mm:ffff8d56199c2640 idx:1 val:-18
I'm sure that this must be the tip of the iceberg of my broken syscall. Thus, before I will dig out the hidden or potential errors, I'd like to know what should be considered when making fork() without CoW or few tips.
The design of the new syscall is based on do_wp_page() -> wp_page_copy() in mm/memory.c. And I only give a change on copy_one_pte() because the calling functions such as copy_pte_range(), copy_pmd_range(), and etc would be the same as far as I thought.
The reason why I chose this function is that it is one of the page faults function to copy a page of CoW. I thought that I could make a similar one but I ended up confronting a lot function that I don't know and I found myself that I don't know how to check my new fork correctly copies all the pages of parents.
You might wonder why I am doing this. I know that fork() without CoW can make the worst performance when it happens. I just wanted to know that how much fast or slow between fork() and fork w/o CoW.
linux kernel x86
asked 6 mins ago
Mr.NobodyMr.Nobody
435
I made a new syscall which is exactly the same as fork() except without CoW. Sadly, I've never experienced hacking the kernel so the new syscall made an error like below.
BUG: Bad rss-counter state mm:ffff8d56199c2640 idx:1 val:-18
I'm sure that this must be the tip of the iceberg of my broken syscall. Thus, before I will dig out the hidden or potential errors, I'd like to know what should be considered when making fork() without CoW or few tips.
The design of the new syscall is based on do_wp_page() -> wp_page_copy() in mm/memory.c. And I only give a change on copy_one_pte() because the calling functions such as copy_pte_range(), copy_pmd_range(), and etc would be the same as far as I thought.
The reason why I chose this function is that it is one of the page faults function to copy a page of CoW. I thought that I could make a similar one but I ended up confronting a lot function that I don't know and I found myself that I don't know how to check my new fork correctly copies all the pages of parents.
You might wonder why I am doing this. I know that fork() without CoW can make the worst performance when it happens. I just wanted to know that how much fast or slow between fork() and fork w/o CoW.
linux kernel x86
linux kernel x86
asked 6 mins ago
Mr.NobodyMr.Nobody
435
asked 6 mins ago
Mr.NobodyMr.Nobody
435
asked 6 mins ago
Mr.NobodyMr.Nobody
435
asked 6 mins ago
Mr.NobodyMr.Nobody
435
asked 6 mins ago
Mr.NobodyMr.Nobody
435
435
add a comment |
add a comment |
0
active
oldest
votes
StackExchange.ready(function() {
var channelOptions = {
tags: "".split(" "),
id: "106"
};
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function() {
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled) {
StackExchange.using("snippets", function() {
createEditor();
});
}
else {
createEditor();
}
});
function createEditor() {
StackExchange.prepareEditor({
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: false,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: null,
bindNavPrevention: true,
postfix: "",
imageUploader: {
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
},
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
});
}
});
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f509792%2fhow-to-implement-fork-without-cow-properly%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
0
active
oldest
votes
0
active
oldest
votes
active
oldest
votes
active
oldest
votes
Thanks for contributing an answer to Unix & Linux Stack Exchange!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function () {
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2funix.stackexchange.com%2fquestions%2f509792%2fhow-to-implement-fork-without-cow-properly%23new-answer', 'question_page');
}
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function () {
StackExchange.helpers.onClickDraftSave('#login-link');
});
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
