Re: [RFC PATCH 0/8] mm/madvise: support process_madvise(MADV_DONTNEED)

[David Hildenbrand]

On 26.09.21 18:12, Nadav Amit wrote:
> From: Nadav Amit <namit@xxxxxxxxxx>
>
> The goal of these patches is to add support for
> process_madvise(MADV_DONTNEED). Yet, in the process some (arguably)
> useful cleanups, a bug fix and performance enhancements are performed.
>
> The patches try to consolidate the logic across different behaviors, and
> to a certain extent overlap/conflict with an outstanding patch that does
> something similar [1]. This consolidation however is mostly orthogonal
> to the aforementioned one and done in order to clarify what is done in
> respect to locks and TLB for each behavior and to batch these operations
> more efficiently on process_madvise().
>
> process_madvise(MADV_DONTNEED) is useful for two reasons: (a) it allows
> userfaultfd monitors to unmap memory from monitored processes; and (b)
> it is more efficient than madvise() since it is vectored and batches TLB
> flushes more aggressively.

MADV_DONTNEED on MAP_PRIVATE memory is a target-visible operation; this 
is very different to all the other process_madvise() calls we allow, 
which are merely hints, but the target cannot be broken . I don't think 
this is acceptable.

--
Thanks,

David / dhildenb