diff options
Diffstat (limited to 'Documentation/vm')
| -rw-r--r-- | Documentation/vm/pagemap.txt | 5 | ||||
| -rw-r--r-- | Documentation/vm/soft-dirty.txt | 36 | ||||
| -rw-r--r-- | Documentation/vm/transhuge.txt | 4 |
3 files changed, 41 insertions, 4 deletions
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 7587493c67f1..5948e455c4d2 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -15,7 +15,8 @@ There are three components to pagemap: * Bits 0-54 page frame number (PFN) if present * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped - * Bits 55-60 page shift (page size = 1<<page shift) + * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt) + * Bits 56-60 zero * Bit 61 page is file-page or shared-anon * Bit 62 page swapped * Bit 63 page present @@ -147,5 +148,5 @@ once. Other notes: Reading from any of the files will return -EINVAL if you are not starting -the read on an 8-byte boundary (e.g., if you seeked an odd number of bytes +the read on an 8-byte boundary (e.g., if you sought an odd number of bytes into the file), or if the size of the read is not a multiple of 8 bytes. diff --git a/Documentation/vm/soft-dirty.txt b/Documentation/vm/soft-dirty.txt new file mode 100644 index 000000000000..9a12a5956bc0 --- /dev/null +++ b/Documentation/vm/soft-dirty.txt @@ -0,0 +1,36 @@ + SOFT-DIRTY PTEs + + The soft-dirty is a bit on a PTE which helps to track which pages a task +writes to. In order to do this tracking one should + + 1. Clear soft-dirty bits from the task's PTEs. + + This is done by writing "4" into the /proc/PID/clear_refs file of the + task in question. + + 2. Wait some time. + + 3. Read soft-dirty bits from the PTEs. + + This is done by reading from the /proc/PID/pagemap. The bit 55 of the + 64-bit qword is the soft-dirty one. If set, the respective PTE was + written to since step 1. + + + Internally, to do this tracking, the writable bit is cleared from PTEs +when the soft-dirty bit is cleared. So, after this, when the task tries to +modify a page at some virtual address the #PF occurs and the kernel sets +the soft-dirty bit on the respective PTE. + + Note, that although all the task's address space is marked as r/o after the +soft-dirty bits clear, the #PF-s that occur after that are processed fast. +This is so, since the pages are still mapped to physical memory, and thus all +the kernel does is finds this fact out and puts both writable and soft-dirty +bits on the PTE. + + + This feature is actively used by the checkpoint-restore project. You +can find more details about it on http://criu.org + + +-- Pavel Emelyanov, Apr 9, 2013 diff --git a/Documentation/vm/transhuge.txt b/Documentation/vm/transhuge.txt index 8785fb87d9c7..4a63953a41f1 100644 --- a/Documentation/vm/transhuge.txt +++ b/Documentation/vm/transhuge.txt @@ -120,8 +120,8 @@ By default kernel tries to use huge zero page on read page fault. It's possible to disable huge zero page by writing 0 or enable it back by writing 1: -echo 0 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page -echo 1 >/sys/kernel/mm/transparent_hugepage/khugepaged/use_zero_page +echo 0 >/sys/kernel/mm/transparent_hugepage/use_zero_page +echo 1 >/sys/kernel/mm/transparent_hugepage/use_zero_page khugepaged will be automatically started when transparent_hugepage/enabled is set to "always" or "madvise, and it'll |