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Diffstat (limited to 'hurd/translator/tmpfs/tmpfs_vs_defpager.mdwn')
| -rw-r--r-- | hurd/translator/tmpfs/tmpfs_vs_defpager.mdwn | 37 |
1 files changed, 37 insertions, 0 deletions
diff --git a/hurd/translator/tmpfs/tmpfs_vs_defpager.mdwn b/hurd/translator/tmpfs/tmpfs_vs_defpager.mdwn index a9317c21..5228515f 100644 --- a/hurd/translator/tmpfs/tmpfs_vs_defpager.mdwn +++ b/hurd/translator/tmpfs/tmpfs_vs_defpager.mdwn @@ -233,3 +233,40 @@ See also: [[open_issues/resource_management_problems/pagers]]. I have never looked at it. [[open_issues/mach-defpager_vs_defpager]]. + + +# IRC, freenode, #hurd, 2011-11-08 + + <mcsim> who else uses defpager besides tmpfs and kernel? + <braunr> normally, nothing directly + <mcsim> than why tmpfs should use defpager? + <braunr> it's its backend + <braunr> backign store rather + <braunr> the backing store of most file systems are partitions + <braunr> tmpfs has none, it uses the swap space + <mcsim> if we allocate memory for tmpfs using vm_allocate, will it be able + to use swap partition? + <braunr> it should + <braunr> vm_allocate just maps anonymous memory + <braunr> anonymous memory uses swap space as its backing store too + <braunr> but be aware that this part of the vm system is known to have + deficiencies + <braunr> which is why all mach based implementations have rewritten their + default pager + <mcsim> what kind of deficiencies? + <braunr> bugs + <braunr> and design issues, making anonymous memory fragmentation horrible + <antrik> mcsim: vm_allocate doesn't return a memory object; so it can't be + passed to clients for mmap() + <mcsim> antrik: I use vm_allocate in pager_read_page + <antrik> mcsim: well, that means that you have to actually implement a + pager yourself + <antrik> also, when the kernel asks the pager to write back some pages, it + expects the memory to become free. if you are "paging" to ordinary + anonymous memory, this doesn't happen; so I expect it to have a very bad + effect on system performance + <antrik> both can be avoided by just passing a real anonymous memory + object, i.e. one provided by the defpager + <antrik> only problem is that the current defpager implementation can't + really handle that... + <antrik> at least that's my understanding of the situation |