linux-kernel - Re: [QUESTION] xas_reload() in iter_xarray_populate

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Message-ID: <918d552a-085a-4529-8f20-a060b1f0c9f1@arm.com>
Date: Tue, 17 Jun 2025 10:40:51 +0530
From: Dev Jain <dev.jain@....com>
To: david@...hat.com, ziy@...dia.com, willy@...radead.org,
 dhowells@...hat.com, hughd@...gle.com
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, ryan.roberts@....com,
 aneesh.kumar@...nel.org
Subject: Re: [QUESTION] xas_reload() in iter_xarray_populate_pages()


On 26/05/25 12:05 pm, Dev Jain wrote:
> Hello all,
>
> After doing an xas_load() and xas_retry(), we take neither a reference nor a lock
> on the folio, and we do an xas_reload(). Is this just to reduce the time window
> for a race?
>
> If the above is true, then, there is a negligible window between xas_load() and
> xas_reload(), because only xas_retry() exists between them, so why to even reload()?
>
> Thanks,
> Dev

I do not completely remember our discussion in THP Cabal; I recall David Howells maybe
saying that the folios are already locked, so it is safe to do xas_load and then do
a folio_get()? Even if we remove the redundant xas_reload(), I still don't understand
why we won't need xas_reload() at least after folio_get()?