On Mon, 01 Jun 2015, Andrew Morton wrote: > On Fri, 29 May 2015 10:13:25 -0400 Eric B Munson <emunson@xxxxxxxxxx> wrote: > > > mlock() allows a user to control page out of program memory, but this > > comes at the cost of faulting in the entire mapping when it is > > allocated. For large mappings where the entire area is not necessary > > this is not ideal. > > > > This series introduces new flags for mmap() and mlockall() that allow a > > user to specify that the covered are should not be paged out, but only > > after the memory has been used the first time. > > I almost applied these, but the naming issue (below) stopped me. > > A few things... > > - The 0/n changelog should reveal how MAP_LOCKONFAULT interacts with > rlimit(RLIMIT_MEMLOCK). > > I see the implementation is "as if the entire mapping will be > faulted in" (for mmap) and "as if it was MCL_FUTURE" (for mlockall) > which seems fine. Please include changelog text explaining and > justifying these decisions. This stuff will need to be in the > manpage updates as well. Change logs are updated, and this will be included in the man page update as well. > > - I think I already asked "why not just use MCL_FUTURE" but I forget > the answer ;) In general it is a good idea to update changelogs in > response to reviewer questions, because other people will be > wondering the same things. Or maybe I forgot to ask. Either way, > please address this in the changelogs. I must have missed that question. Here is the text from the updated mlockall changelog: MCL_ONFAULT is preferrable to MCL_FUTURE for the use cases enumerated in the previous patch becuase MCL_FUTURE will behave as if each mapping was made with MAP_LOCKED, causing the entire mapping to be faulted in when new space is allocated or mapped. MCL_ONFAULT allows the user to delay the fault in cost of any given page until it is actually needed, but then guarantees that that page will always be resident. > > - I can perhaps see the point in mmap(MAP_LOCKONFAULT) (other > mappings don't get lock-in-memory treatment), but what's the benefit > in mlockall(MCL_ON_FAULT) over MCL_FUTURE? (Add to changelog also, > please). > > - Is there a manpage update? I will send one out when I post V2 > > - Can we rename patch 1/3 from "add flag to ..." to "add mmap flag to > ...", to distinguish from 2/3 "add mlockall flag ..."? Done > > - The MAP_LOCKONFAULT versus MCL_ON_FAULT inconsistency is > irritating! Can we get these consistent please: switch to either > MAP_LOCK_ON_FAULT or MCL_ONFAULT. Yes, will do for V2. >
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