tmpfs: limit regularFile.Translate() fill range #11343
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When e.g. an application thread takes a page fault on an mmapped file, MM calls `memmap.Mappable.Translate()` to obtain the corresponding host FD range that should be mapped into the application's address space. It passes both the range that *must* be mapped (e.g. the faulting page) as `required`, and the maximum range that *may* be mapped (the previously-unfaulted part of the corresponding VMA) as `optional`, such that file implementations can map more than `required` to avoid future page faults. Prior to this CL, `tmpfs.regularFile.Translate()` always returned translations up to `optional`, under the assumption that allocating larger ranges from `pgalloc.MemoryFile` has negligible incremental cost. This behavior dates to the introduction of `memmap.Mappable.Translate()` (cl/182882705) and thus predates the implementation of tmpfs size limits (cl/442686814). Now that the latter exists, unconditionally translating - and therefore allocating pages - up to `optional` can result in hitting tmpfs size limits prematurely. Thus: Constrain optional translations returned by `tmpfs.regularFile.Translate()`, applying the same logic as `gofer.maxFillRange()`. PiperOrigin-RevId: 713134287
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tmpfs: limit regularFile.Translate() fill range
When e.g. an application thread takes a page fault on an mmapped file, MM calls
memmap.Mappable.Translate()to obtain the corresponding host FD range thatshould be mapped into the application's address space. It passes both the range
that must be mapped (e.g. the faulting page) as
required, and the maximumrange that may be mapped (the previously-unfaulted part of the corresponding
VMA) as
optional, such that file implementations can map more thanrequiredto avoid future page faults.
Prior to this CL,
tmpfs.regularFile.Translate()always returned translationsup to
optional, under the assumption that allocating larger ranges frompgalloc.MemoryFilehas negligible incremental cost. This behavior dates tothe introduction of
memmap.Mappable.Translate()(cl/182882705) and thuspredates the implementation of tmpfs size limits (cl/442686814). Now that the
latter exists, unconditionally translating - and therefore allocating pages -
up to
optionalcan result in hitting tmpfs size limits prematurely.Thus: Constrain optional translations returned by
tmpfs.regularFile.Translate(), applying the same logic asgofer.maxFillRange().