How many page table the linux kernel maintains?
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the kernel maintains a data structure, called a page table, that contains a mapping of
a processes' virtual page addresses to real page addresses in memory.
I read a book with the sentence above, I don't know why it's a processes'? So the kernel
has a single page table which contains mappings for many processes, i.e. kernel didn't store those page tables for all processes separately, but in a single page table?
The book is How Linux Works by Brian Ward, 2nd, page 182, line 4.
It seems like the book has some grammar errors:
table, that should be table that: no error. (thanks for the comment!)
a mapping of a processes' should be a mapping of a process's
linux linux-kernel
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up vote
0
down vote
favorite
the kernel maintains a data structure, called a page table, that contains a mapping of
a processes' virtual page addresses to real page addresses in memory.
I read a book with the sentence above, I don't know why it's a processes'? So the kernel
has a single page table which contains mappings for many processes, i.e. kernel didn't store those page tables for all processes separately, but in a single page table?
The book is How Linux Works by Brian Ward, 2nd, page 182, line 4.
It seems like the book has some grammar errors:
table, that should be table that: no error. (thanks for the comment!)
a mapping of a processes' should be a mapping of a process's
linux linux-kernel
asked 2 days ago
ptr_user7813604
1186
New contributor
ptr_user7813604 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
2
“... a data structure, called a page table, that ...” is correct: “that” refers to “a data structure”.
– Stephen Kitt
2 days ago
@StephenKitt: That makes sense, thank you!
– ptr_user7813604
2 days ago
add a comment |
up vote
0
down vote
favorite
up vote
0
down vote
favorite
the kernel maintains a data structure, called a page table, that contains a mapping of
a processes' virtual page addresses to real page addresses in memory.
I read a book with the sentence above, I don't know why it's a processes'? So the kernel
has a single page table which contains mappings for many processes, i.e. kernel didn't store those page tables for all processes separately, but in a single page table?
The book is How Linux Works by Brian Ward, 2nd, page 182, line 4.
It seems like the book has some grammar errors:
table, that should be table that: no error. (thanks for the comment!)
a mapping of a processes' should be a mapping of a process's
linux linux-kernel
asked 2 days ago
ptr_user7813604
1186
New contributor
ptr_user7813604 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
the kernel maintains a data structure, called a page table, that contains a mapping of
a processes' virtual page addresses to real page addresses in memory.
I read a book with the sentence above, I don't know why it's a processes'? So the kernel
has a single page table which contains mappings for many processes, i.e. kernel didn't store those page tables for all processes separately, but in a single page table?
The book is How Linux Works by Brian Ward, 2nd, page 182, line 4.
It seems like the book has some grammar errors:
table, that should be table that: no error. (thanks for the comment!)
a mapping of a processes' should be a mapping of a process's
linux linux-kernel
linux linux-kernel
asked 2 days ago
ptr_user7813604
1186
New contributor
ptr_user7813604 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.
asked 2 days ago
ptr_user7813604
1186
New contributor
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edited 2 days ago
asked 2 days ago
ptr_user7813604
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ptr_user7813604 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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asked 2 days ago
ptr_user7813604
1186
asked 2 days ago
ptr_user7813604
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New contributor
ptr_user7813604 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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2
“... a data structure, called a page table, that ...” is correct: “that” refers to “a data structure”.
– Stephen Kitt
2 days ago
@StephenKitt: That makes sense, thank you!
– ptr_user7813604
2 days ago
add a comment |
2
“... a data structure, called a page table, that ...” is correct: “that” refers to “a data structure”.
– Stephen Kitt
2 days ago
@StephenKitt: That makes sense, thank you!
– ptr_user7813604
2 days ago
2
2
“... a data structure, called a page table, that ...” is correct: “that” refers to “a data structure”.
– Stephen Kitt
2 days ago
“... a data structure, called a page table, that ...” is correct: “that” refers to “a data structure”.
– Stephen Kitt
2 days ago
@StephenKitt: That makes sense, thank you!
– ptr_user7813604
2 days ago
@StephenKitt: That makes sense, thank you!
– ptr_user7813604
2 days ago
add a comment |
1 Answer
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It's a bit more complicated than that.
First off, there is only one true page table for any given processor core at a time. This is because it's the hardware that does the actual mapping of virtual addresses to physical addresses (more specifically, the MMU), and the kernel only ever gets involved when the contents of the page table have to change.
In addition, the kernel stores it's own information about the state of the virtual memory mappings for each execution context (process, thread, or kernel thread) separately. These are stored independently of each other and separate from the page tables used by the hardware for address mapping. Whenever the execution context changes (for example, a process makes a system call or an interrupt handler gets woken up to service an interrupt), part of the process of switching the execution context involves flushing the old entries from the hardware page table, and then loading it with the new entries. Depending on the two contexts, this may involve only repopulating a very small number of entries (for example, switching threads of the same userspace process), or it might require reloading the entire table (for example, switching from a user process to an interrupt handler).
answered 2 days ago
Austin Hemmelgarn
5,89811016
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
1
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
add a comment |
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1 Answer
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1 Answer
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It's a bit more complicated than that.
First off, there is only one true page table for any given processor core at a time. This is because it's the hardware that does the actual mapping of virtual addresses to physical addresses (more specifically, the MMU), and the kernel only ever gets involved when the contents of the page table have to change.
In addition, the kernel stores it's own information about the state of the virtual memory mappings for each execution context (process, thread, or kernel thread) separately. These are stored independently of each other and separate from the page tables used by the hardware for address mapping. Whenever the execution context changes (for example, a process makes a system call or an interrupt handler gets woken up to service an interrupt), part of the process of switching the execution context involves flushing the old entries from the hardware page table, and then loading it with the new entries. Depending on the two contexts, this may involve only repopulating a very small number of entries (for example, switching threads of the same userspace process), or it might require reloading the entire table (for example, switching from a user process to an interrupt handler).
answered 2 days ago
Austin Hemmelgarn
5,89811016
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
1
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
add a comment |
up vote
1
down vote
It's a bit more complicated than that.
First off, there is only one true page table for any given processor core at a time. This is because it's the hardware that does the actual mapping of virtual addresses to physical addresses (more specifically, the MMU), and the kernel only ever gets involved when the contents of the page table have to change.
In addition, the kernel stores it's own information about the state of the virtual memory mappings for each execution context (process, thread, or kernel thread) separately. These are stored independently of each other and separate from the page tables used by the hardware for address mapping. Whenever the execution context changes (for example, a process makes a system call or an interrupt handler gets woken up to service an interrupt), part of the process of switching the execution context involves flushing the old entries from the hardware page table, and then loading it with the new entries. Depending on the two contexts, this may involve only repopulating a very small number of entries (for example, switching threads of the same userspace process), or it might require reloading the entire table (for example, switching from a user process to an interrupt handler).
answered 2 days ago
Austin Hemmelgarn
5,89811016
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
1
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
add a comment |
up vote
1
down vote
up vote
1
down vote
It's a bit more complicated than that.
First off, there is only one true page table for any given processor core at a time. This is because it's the hardware that does the actual mapping of virtual addresses to physical addresses (more specifically, the MMU), and the kernel only ever gets involved when the contents of the page table have to change.
In addition, the kernel stores it's own information about the state of the virtual memory mappings for each execution context (process, thread, or kernel thread) separately. These are stored independently of each other and separate from the page tables used by the hardware for address mapping. Whenever the execution context changes (for example, a process makes a system call or an interrupt handler gets woken up to service an interrupt), part of the process of switching the execution context involves flushing the old entries from the hardware page table, and then loading it with the new entries. Depending on the two contexts, this may involve only repopulating a very small number of entries (for example, switching threads of the same userspace process), or it might require reloading the entire table (for example, switching from a user process to an interrupt handler).
answered 2 days ago
Austin Hemmelgarn
5,89811016
It's a bit more complicated than that.
First off, there is only one true page table for any given processor core at a time. This is because it's the hardware that does the actual mapping of virtual addresses to physical addresses (more specifically, the MMU), and the kernel only ever gets involved when the contents of the page table have to change.
In addition, the kernel stores it's own information about the state of the virtual memory mappings for each execution context (process, thread, or kernel thread) separately. These are stored independently of each other and separate from the page tables used by the hardware for address mapping. Whenever the execution context changes (for example, a process makes a system call or an interrupt handler gets woken up to service an interrupt), part of the process of switching the execution context involves flushing the old entries from the hardware page table, and then loading it with the new entries. Depending on the two contexts, this may involve only repopulating a very small number of entries (for example, switching threads of the same userspace process), or it might require reloading the entire table (for example, switching from a user process to an interrupt handler).
answered 2 days ago
Austin Hemmelgarn
5,89811016
edited 2 days ago
answered 2 days ago
Austin Hemmelgarn
5,89811016
answered 2 days ago
Austin Hemmelgarn
5,89811016
answered 2 days ago
Austin Hemmelgarn
5,89811016
5,89811016
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
1
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
add a comment |
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
1
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I don't quite understand your Independent of that, ... and from the hardware page table, could you elaborate more? (especially the both from each other.)
– ptr_user7813604
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
I've updated the answer to hopefully clarify things better. Sorry that it was a bit confusing.
– Austin Hemmelgarn
2 days ago
1
1
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
In the last sentence, reloading the entire table used to be rare (or at least, it could have been made rare, since the kernel mapping didn’t change), and switching from a user process to the kernel didn’t involve touching the page table; all that changed with KAISER/KPTI.
– Stephen Kitt
2 days ago
add a comment |
ptr_user7813604 is a new contributor. Be nice, and check out our Code of Conduct.
ptr_user7813604 is a new contributor. Be nice, and check out our Code of Conduct.
ptr_user7813604 is a new contributor. Be nice, and check out our Code of Conduct.
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2
“... a data structure, called a page table, that ...” is correct: “that” refers to “a data structure”.
– Stephen Kitt
2 days ago
@StephenKitt: That makes sense, thank you!
– ptr_user7813604
2 days ago