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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Proofpoint-GUID: SuEf-5nOqWGOI0hJgzj5aA67P-zFvCG0 X-Proofpoint-ORIG-GUID: SuEf-5nOqWGOI0hJgzj5aA67P-zFvCG0 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTExMDE5NCBTYWx0ZWRfX/ObQG/oyX7h7 Q4qvi4caa2m7hhOM37evW/8INOUL64QEc3U/HcroDHYGdYu13E3VKsURYxcsgZvsx/glCMp5TJ1 O3cs93wATV/nNgzpP2nBvwcLfi1YhgVZzdsYdDp4MRNQ4vEBl/ux4kQ5QSJyBG5Iz9rWbxt9GoV K2cmpqPH1fKZ4ilvT4BaODDtjrceyiAR6HLLoUMP2zYjudq1gjvLftLEiBexhQG4Xf0ZFSE5HUV yXDGJLz2MRYwFXttxVjB2HB+jwVLYcTnWrA0zVZUSfCjHoaVFxp6QYEQKsrdH+/XX/V2LVKFsDb QR3G1C4XtwvvRFvqPpxReZ78FsuMyFnoQGiBY5OYqqJ5dZ26oBQRaCtcHVxGgefCDGbpF68QLDV 7AALofHeR3g+PD0cA1CSqxBkqIrODpllXHMp5F344xpxZ00VF1+FK4Sioys9ZUc+5+suVI2T9mS WF/eh7Djk6FOthqYCdw== X-Authority-Analysis: v=2.4 cv=Eeb4hvmC c=1 sm=1 tr=0 ts=6a021ccf cx=c_pps a=72HoHk1woDtn7btP4rdmlg==:117 a=uvjyHnA+wHnVBzamt/20/A==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=x7bEGLp0ZPQA:10 a=VkNPw1HP01LnGYTKEx00:22 a=Da8U98TiO7q1upZEImrf:22 a=svvvyxlR1OQQkelhaPoB:22 a=5NEz3i_17GglibqS5w4A:9 a=QEXdDO2ut3YA:10 a=kA6IBgd4cpdPkAWqgNAz:22 X-Proofpoint-Virus-Version: vendor=nai engine=6800 definitions=11783 signatures=596817 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 impostorscore=10 malwarescore=0 priorityscore=1501 clxscore=1015 lowpriorityscore=10 suspectscore=0 bulkscore=10 adultscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605110194 On 5/11/26 12:26 PM, Jan Kara wrote: > On Mon 11-05-26 13:44:17, Vishal Moola wrote: >> On Sun, May 10, 2026 at 05:54:17PM -0400, Tal Zussman wrote: >> > page_cache_prev_miss() is documented to return a value outside the >> > searched range when no gap is found. However, the no-gap-found path >> > returns xas.xa_index, which after a successful loop is the first index >> > in the range. As such, that index is misreported as a gap. >> > >> > The sole caller, page_cache_sync_ra(), uses the return value to estimate >> > the cached run preceding a sequential read. In some cases, the buggy >> > return value can undercount the contiguous range by one, shrinking the >> > readahead window or pushing borderline requests into the >> > small-random-read branch. >> > >> > Mirror the fix in commit bbcaee20e03e ("readahead: fix return value of >> > page_cache_next_miss() when no hole is found"): preserve max_scan in a >> > separate variable across the loop and return `index - max_scan` from the >> > no-gap-found path. >> >> IMO, this way of fixing it hurts the readability. I'd prefer something >> similar to the fix in the original commit. Or... >> >> > - while (max_scan--) { >> > + while (nr--) { >> > void *entry = xas_prev(&xas); >> > if (!entry || xa_is_value(entry)) >> > - break; >> > + return xas.xa_index; >> > if (xas.xa_index == ULONG_MAX) >> > - break; >> > + return ULONG_MAX; >> > } >> >> If I understand this correctly, couldn't we just do something like: >> if (!max_scan) >> return xas.xa_index - 1; > > I think the easiest to understand would be to do the above two explicit > returns instead of 'break' and change below to: > > /* Return start of the range - 1 when no hole is found */ > return xas.xa_index - 1; I can do that, but I think it should be consistent with page_cache_next_miss(), which does index + max_scan. If the xas.xa_index approach is preferred, I'll change it in both functions, and also get rid of nr. The nice part of 'index - max_scan' is that the kdoc describes the range in terms of that already. Thoughts? >> > - return xas.xa_index; >> > + return index - max_scan; >> > }